Golden, bubbly, and impossibly cheesy — this Cheesy Potato Gratin Casserole hits every comfort-food note and still looks fancy enough for company.

Hey friend — if you want a dish that makes people swoon without requiring Michelin-level skills, this is it. I grew up watching my dad make something like this for holidays, and I still make it when I want to impress with very little stress. Let’s walk through why this gratin works, what gear you actually need, the full recipe (scaled to serve 8), calories, and a few tricks that’ll make it turn out perfect every time.

Quick facts you’ll want to know

Prep Time: 30 minutes
Cook Time: 1 hour 15 minutes
Total Time: 1 hour 45 minutes
Serves: 8
Estimated Calories per Serving: 256 kcal (approx.)

Why this gratin wins

Roasting or baking sliced Yukon Golds in a rich cheese sauce gives you a creamy texture and a crunchy top. Yukon Gold potatoes deliver buttery flavor and hold their shape, so the casserole stays silky without turning into glue. Cheddar gives bite, while Gruyère and Parmesan on top add nuttiness and that postcard-worthy golden crust. Want restaurant vibes at home? This is your ticket. IMO, simple ingredients + patient baking = magic. 🙂

Ingredients (for 8 servings — use exactly these for best results)

Potatoes & Veg:

2½ pounds Yukon Gold potatoes (6–7 medium), sliced into 1/8-inch rounds
½ medium yellow onion, thinly sliced

Sauce:

3 tbsp salted butter
¼ cup all-purpose flour
1½ cups whole milk or unsweetened almond milk (for lighter or dairy-free-ish)
8 oz sharp Cheddar (about 2 cups, shredded)
¾ tsp kosher salt, plus more to taste
½ tsp garlic powder
Freshly ground black pepper, to taste

Toppings:

2 oz shredded Gruyère (½ cup)
2 oz grated Parmesan (½ cup)
Chopped fresh chives or parsley for garnish

Bold tip: Slice potatoes uniformly (use a mandoline if you have one) so they cook evenly.

Equipment (you actually need these)

9-inch square baking dish (or similar 8×8–9×13 if you prefer thinner layers)
Large pot or saucepan for the sauce
Mandoline or sharp chef’s knife for even slices
Whisk
Measuring cups & spoons
Aluminum foil and oven mitts

FYI: You don’t need expensive tools. A steady hand and a sharp knife work fine — but the mandoline speeds things up and keeps slices pretty.

Full recipe — step-by-step (follow this and breathe easy)

1. Preheat & prep

Preheat your oven to 375°F (190°C). Spray a 9-inch square baking dish with cooking spray. Peel (or scrub) and slice the potatoes into 1/8-inch rounds, then slice the onion thinly. Arrange potatoes in the prepared dish in three or four rows, leaving a little space so the slices sit slightly slanted. Tuck onion slices between and on top of the potatoes wherever they fit.

2. Make the cheese sauce

Melt 3 tbsp butter in a medium pot over medium heat. Whisk in ¼ cup flour and cook while whisking for about 30 seconds so the raw flour taste disappears. Slowly stream in 1½ cups milk, whisking constantly to avoid lumps. Raise the heat to medium-high and bring the mixture to a boil, then reduce to medium-low and simmer until the sauce thickens to a creamy gravy, about 5 minutes. Reduce heat to low and stir in 8 oz sharp Cheddar, ¾ tsp kosher salt, ½ tsp garlic powder, and a few grinds of pepper. Taste and adjust salt and pepper if needed.

3. Assemble & bake (first stage)

Pour the sauce evenly over the arranged potatoes and onions. Cover the pan tightly with foil and bake 45 minutes. This steam-phase softens the potatoes and lets the flavors meld.

4. Top & finish baking

Remove the foil and sprinkle Gruyère and Parmesan evenly over the top. Return the dish to the oven and bake, uncovered, until the potatoes pierce easily with a fork and the top turns golden brown, 30–45 minutes. For a super-crispy finish, switch the oven to broil for 1–2 minutes — watch closely so it doesn’t burn.

5. Rest & serve

Allow the gratin to cool 10 minutes so it sets slightly. Garnish with chopped chives or parsley and serve warm.

Make-ahead & storage (real-life tested)

To make ahead: Assemble the gratin up through pouring the sauce, then cover with foil and refrigerate up to 1 day. Add 10–15 minutes to the baking time when you bake from chilled.
To store: Keep leftovers in an airtight container in the fridge up to 5 days.
To reheat: Microwave in 30-second bursts until warm, or reheat in a 350°F oven covered for 15–20 minutes. For crisp top, remove foil and broil briefly.

Substitutions & variations (because variety keeps things fun)

Gluten-free: Use 1:1 gluten-free flour instead of AP flour.
Add protein: Sprinkle ½ cup chopped cooked bacon or ham between layers, or stir into the sauce (Dad’s ham & cheese trick — total crowd-pleaser).
Lighter dairy: Use unsweetened almond milk and a reduced-fat cheddar; the texture will still be lovely.
More depth: Add a pinch of nutmeg to the sauce for a subtle cozy note.

Some Problems (quick fixes)

Sauce lumpy? Whisk vigorously while it warms or strain quickly.
Top browning too fast? Tent with foil and continue baking until fork-tender.
Potatoes undercooked after time? Bake uncovered longer; oven temperatures vary.

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Nutrition snapshot (per serving, approx.)

Calories: 256 kcal
Carbohydrates: 24 g
Protein: 13.2 g
Fat: 12.6 g (Saturated Fat: 7.3 g)
Fiber: 3.5 g
Sugar: 1.6 g

Yes, cheese exists here — but the potato gives you good carbs and the dish still fits into balanced family meals. Want fewer calories? Serve smaller portions and pair with a big green salad.

Serving suggestions (pairings that sing)

Simple green salad with lemon vinaigrette (bright contrast).
Roasted Brussels sprouts or garlicky green beans.
Sliced roast chicken or a smoky grilled tempeh for a fuller plate.
Wine pairing: a crisp Chardonnay or light red like Pinot Noir complements the cheese.

Why this method works (a quick nerdy note)

Layering thin slices lets heat penetrate evenly while the cheese-thickened sauce seeps between layers. Covering first traps steam and softens potatoes; finishing uncovered creates that picture-perfect golden crust. Ever wonder why gratins taste restaurant-level? They balance creaminess and crispness in a very satisfying way.

Final mom-tested tips (my favorites)

Slice thin and even — uniform slices equal even cooking.
Don’t skimp on resting time. Ten minutes makes the gratin cut nicely.
Use sharp cheddar for flavor bite; older cheddars add more depth.
Label leftovers with date — you’ll forget and find magic in the fridge later.

My Opening

So there you go: a Cheesy Potato Gratin Casserole that looks fancy but cooks itself into comfort. Try it for holiday dinners or any night you want that warm, cheesy hug on a plate. Will you go classic or throw in Dad’s ham twist? Either way, send me a picture — I judge gratins by how much cheese bubbles over the edge