Old Fashioned Cheese Potato Onion Casserole
This casserole is a nostalgic embrace from the past—simple ingredients layered with love and flavor.
Creamy, rustic potatoes meld with sweet caramelized onions, sharp cheddar, and earthy thyme to create a dish that feels like home.
Whether served as a humble side or the comforting star of the meal, it’s a timeless recipe that speaks to generations and warms the soul with every bite.
Why People Will Love This Old Fashioned Cheese Potato Onion Casserole:
Nostalgic comfort: This dish evokes warm childhood memories and the flavors of a simpler time—just like something Grandma would make on a chilly evening.
Rich layers of flavor: The sweetness of golden sautéed onions perfectly balances the earthy richness of mashed potatoes and the sharpness of aged cheddar cheese.
Simple, humble ingredients: It transforms everyday staples like potatoes, onions, and butter into a deeply satisfying, soul-warming dish.
Versatile and crowd-pleasing: Whether served as a side at holiday dinners or as a main course on busy weeknights, it satisfies all appetites and fits any occasion.
Texture you can savor: The contrast of soft, chunky mashed potatoes and melted bubbly cheese creates a rustic, hearty mouthfeel that keeps people coming back for seconds.
Key Ingredients:
Potatoes – The heart of the dish. Russet or Yukon Gold potatoes bring a starchy richness and creamy texture that form the foundation of this rustic casserole. When mashed with care, they create the perfect canvas for other flavors to shine.
Onions – Slowly sautéed until golden and tender, onions offer a naturally sweet and savory depth that weaves through every bite, adding warmth and aromatic complexity.
Cheddar cheese – Aged sharp cheddar, either white or orange, melts into the top layer, creating a golden, bubbling crust that adds bold tanginess and creamy richness with each forkful.
Unsalted butter – Melted into the onions and mixed with the potatoes, butter lends a silky finish and comforting mouthfeel that makes this dish feel truly indulgent.
Dried thyme – Just a touch of this earthy herb gives a subtle woodsy note, enhancing the rustic profile and adding dimension without overpowering the simplicity of the ingredients.
Expert Tips:
Use a blend of potato textures for depth
Combining Russet (fluffy) and Yukon Gold (creamy) potatoes creates a balanced bite—light yet buttery. It gives the casserole structure and richness without becoming too dense.
Don’t over-mash the potatoes
Leave some chunky bits when mashing. Overworking the potatoes can release too much starch, resulting in a gummy texture. A rustic, hand-mashed finish creates comforting contrast.
Caramelize the onions slowly
Take your time when sautéing the onions—low and slow brings out their natural sweetness and umami depth. Rushing this step leads to bitterness rather than the soft golden tenderness you want.
Season in layers, not just at the end
Add kosher salt and black pepper to the boiling water, to the potato mash, and again when combining the onions and thyme. This layering builds complexity and avoids a flat-tasting final dish.
Let it rest before serving
Once baked, allow the casserole to rest for 5–10 minutes. This lets the cheese set slightly and allows the flavors to meld, making for cleaner slices and a more cohesive bite.
Old Fashioned Cheese Potato Onion Casserole
Ingredients
3 pounds russet or Yukon Gold potatoes, peeled and cut into chunks
2 tablespoons unsalted butter
2 large yellow onions, finely diced
1 teaspoon dried thyme
2 ounces sharp cheddar cheese (white or orange), grated
Kosher salt and freshly ground black pepper, to taste
Instructions
Preheat the oven:
Set your oven to 375°F (190°C).
Lightly grease a 9×9-inch baking dish with cooking spray or butter and set aside.
Cook the potatoes:
Place the peeled and chopped potatoes into a large stockpot.
Cover with water and add a generous amount of salt.
Bring to a boil over medium-high heat and cook until the potatoes are fork-tender.
Drain well and transfer to a large mixing bowl.
Roughly mash the potatoes using a fork or potato masher—leave a few chunks for texture.
Sauté the onions:
In a medium skillet, melt the butter over medium heat.
Add the diced onions and cook until they are soft and golden brown, about 8–10 minutes.
Add the sautéed onions to the mashed potatoes.
Season and mix:
Stir in the dried thyme along with salt and freshly cracked black pepper to taste.
Mix until well combined.
Assemble the casserole:
Spoon the potato-onion mixture into the prepared baking dish.
Sprinkle the grated cheddar cheese evenly over the top.
Bake:
Bake in the preheated oven for 15 to 20 minutes, or until the cheese is melted, bubbly, and lightly golden on top.
Serve:
Let the casserole rest for a few minutes after baking, then serve warm.
Enjoy as a comforting side or main dish!
Important Notes When Making Old Fashioned Cheese Potato Onion Casserole:
Potato choice matters
Stick to starchy or semi-waxy varieties like Russet or Yukon Gold. Russets absorb flavors well and create a fluffy base, while Yukon Golds add creaminess. Avoid red potatoes—they can be too waxy and resist mashing.
Drain and dry thoroughly
After boiling, drain the potatoes well and let them steam off excess moisture. Any remaining water can make the casserole soggy and dilute the flavor.
Onion texture should be soft, not crispy
Cook the onions until golden and translucent, not browned or crispy. Their melt-in-your-mouth softness complements the mashed potatoes and avoids overpowering the dish with harsh onion flavor.
Cheese adds flavor, not stretch
This dish is about flavorful richness, not gooey texture. Use a sharp cheddar and grate it fresh—pre-shredded cheese contains anti-caking agents that can interfere with melting.
Season with intention
The ingredients are simple, so seasoning is key. Be generous with salt during boiling, and taste the mixture before baking to ensure balance. Even a pinch more black pepper or thyme can deepen the overall flavor.
How To Enjoy Old Fashioned Cheese Potato Onion Casserole After Cooking:
Let it rest before serving
After removing the casserole from the oven, let it sit for 5–10 minutes. This allows the melted cheese to settle, and the flavors to marry. It also firms up slightly for cleaner slicing and serving.
Serving suggestions
As a side dish:
Pair it with roasted meats like herb-crusted chicken, meatloaf, baked ham, or pot roast. The creamy potatoes and sweet onions balance out rich proteins beautifully.
As a main:
Serve it with a crispy green salad dressed in vinaigrette or steamed greens (like kale or spinach) for contrast. A fried egg on top makes it a rustic vegetarian main.
Enhance with toppings
Add a pat of butter, a drizzle of herb-infused oil, or a dollop of sour cream or crème fraîche for an extra creamy bite.
Garnish with chopped chives, parsley, or caramelized onions to elevate presentation and add flavor contrast.
How to store and reheat
Refrigerate leftovers in an airtight container for up to 4 days.
To reheat, cover with foil and warm in a 325°F (165°C) oven for 15–20 minutes until heated through. You can also reheat individual servings in the microwave (about 2–3 minutes), but the oven preserves the texture best.
Bonus tip:
For a next-day twist, fry leftover slices in a nonstick pan until golden on both sides. It creates a crispy crust and is excellent for breakfast with eggs or as a hearty lunch with soup.
Nutrition Information
Per serving for the Old Fashioned Cheese Potato Onion Casserole, assuming 6 servings:
Calories: 190 kcal | Total Fat: 7.8 g | Saturated Fat: 4.3 g | Monounsaturated Fat: 1.8 g | Polyunsaturated Fat: 0.5 g | Cholesterol: 20 mg | Sodium: 280–350 mg (depending on added salt) | Total Carbohydrates: 26.5 g | Dietary Fiber: 3.2 g | Sugars: 3.1 g | Protein: 4.5 g
Frequently Asked Questions:
Can I make this casserole ahead of time?
Yes! You can prepare the mashed potato-onion mixture and assemble the casserole (without baking) up to 24 hours in advance. Cover and refrigerate, then bake just before serving. Add 5–10 minutes to the baking time if starting cold from the fridge.
What type of potatoes work best for this casserole?
Both russet and Yukon Gold potatoes work well. Russets are fluffier and absorb flavors beautifully, while Yukon Golds have a naturally buttery texture and hold their shape better, adding more creaminess and body.
Can I substitute a different cheese?
Absolutely. While sharp cheddar is traditional and adds rich flavor, you can experiment with Gruyère, Monterey Jack, or even a smoked cheese for a twist. Just make sure it’s a good melting cheese.
How do I make this recipe more filling for a main dish?
To turn it into a heartier main, consider mixing in cooked crumbled bacon, ground sausage, or even shredded rotisserie chicken before baking. A handful of frozen peas or sautéed spinach can also add nutrition.
Is it possible to make this recipe vegetarian or vegan?
Yes. For a vegetarian version, ensure your cheese and butter are free of animal rennet. For a vegan version, use plant-based butter, vegan shredded cheese, and non-dairy milk if mashing with a little liquid. The flavor will differ slightly but still be comforting.
How finely should I mash the potatoes?
Leave the potatoes slightly chunky for a rustic texture. Over-mashing can make the casserole gluey. A fork or potato masher works best—avoid electric mixers.
Can I sauté the onions ahead of time?
Yes. You can sauté the onions up to 2 days in advance. Store them in an airtight container in the fridge. This is a great time-saver for prep day.
What’s the best way to ensure even cheese melting on top?
Use freshly grated cheese instead of pre-shredded. Pre-packaged cheese often contains anti-caking agents that prevent smooth melting and browning.
How can I prevent a watery casserole?
Drain the potatoes thoroughly after boiling, and pat them dry if necessary. Avoid using waxy potatoes like red or new potatoes, which release more moisture when baked.
Can I double the recipe for a larger crowd?
Yes. Double all ingredients and bake in a 9×13-inch dish. Increase the baking time by about 10 minutes, checking for bubbling cheese and golden edges as your cue it’s done.