Caramelized Onion Scalloped Potatoes

This is the kind of cozy, slightly sinful side dish that shows up at our table every time the weather tilts toward sweater season — thinly sliced potatoes folded into a creamy, cheesy sauce, studded with deeply caramelized onions that taste like little bites of buttery magic. It’s sticky, soft, and unapologetically rich, but also exactly what you want when you need comfort food that feels thoughtful (and a tiny bit fancy) without actually trying too hard.

My husband calls this “the casserole that steals the show.” He’ll scrape the edges with a fork like it’s a sport and then ask if there are enough leftovers for breakfast (there always are). Our kid once announced, mid-bite, “This is like mashed potatoes but better,” and I leaned into that and made it a regular. It’s become our go-to for dinners when we want something that feeds a crowd, reheats well, and makes everyone stop and take a breath. I’ve burned the bottom twice and learned to watch the oven like a hawk, but that only made the first perfect slice taste sweeter.

Kitchen Talk

MORE EASY SIDE DISHES RECIPES...

SIDE DISHES

Creamy Parmesan Polenta Recipe

SIDE DISHES

Easy Home Fries Recipe

SIDE DISHES

Carrot Salad with Raisins Recipe

SIDE DISHES

Garlic Roasted Potatoes and Veggies

Okay, full disclosure: the first time I tried to caramelize the onions and then slice potatoes paper-thin I totally overcooked one and undercooked the other. Lesson learned — low and slow for onions (a little patience goes a long way), and use a mandoline or a very sharp knife for even potato layers. I once swapped half the milk for light cream on a whim and the sauce turned out silkier and more forgiving, so that stayed. Also, I will shamefully admit to sprinkling a little extra cheddar on top under the broiler. No regrets.

Shopping Tips

– Vegetables: Pick starchy potatoes like Yukon Gold or Russets — they hold shape but become creamy when baked. Avoid waxy red potatoes here.
– Dairy: Whole milk and a little cream make the sauce lush; skim is too thin. If you want lighter, mix milk with a splash of half-and-half.
– Cheese: Sharp cheddar or gruyère add flavor depth; pre-shredded is fine in a pinch but freshly grated melts better.
– Fats & Oils: Use real butter for sautéing the onions — it adds sweetness and helps them brown properly. Olive oil alone won’t give the same flavor.
– Spices: Keep it simple with salt, pepper, and a little nutmeg or thyme if you like earthiness; fresh herbs are optional but nice.

Prep Ahead Ideas

– Slice the potatoes and store them submerged in cold water in the fridge for up to 24 hours to prevent browning.
– Caramelize the onions a day ahead; they reheat beautifully and actually deepen in flavor overnight. Store in a sealed container.
– Grate cheese and measure spices into a small container so assembly is a one-pan job at dinner time.

✔Time-Saving Tricks

– Use a mandoline to slice potatoes thin and even — saves time and ensures even cooking.
– Buy pre-shredded cheese if you’re in a rush, but toss it in a bowl with a pinch of cornstarch so it behaves like fresh.
– Short on time? Part-cook the potato slices in the microwave for a few minutes to jump-start tenderness before baking.
– Don’t rush the onions if you can help it — the payoff is worth the extra 10–20 minutes.

✔Common Mistakes

– Not slicing potatoes evenly: I eyeballed them once and got a crunchy layer in the middle — use a mandoline or sharp knife.
– Sauce too thin: if it’s watery after baking, pop it back in the oven uncovered to reduce, or stir in a tiny slurry of cornstarch and warm it on the stovetop.
– Burning the onions: high heat is tempting but low-and-slow is the only way to get that golden-sweet flavor without char.
– Overbaking the edges: tent with foil if the top is browning before the potatoes are tender.

What to Serve It With

– A bright, acidic salad with lemon vinaigrette to cut through the richness.
– Roasted or pan-seared chicken for a classic, cozy pairing.
– Simple steamed greens like green beans or sautéed spinach.
– Crusty bread to mop up the cheesy sauce.

✔Tips & Mistakes

– Use even slices — your oven won’t save uneven potato thickness.
– Salt layers lightly as you stack so the seasoning is even throughout.
– If the top browns too fast, tent with foil and finish until potatoes are tender.
– Forgot to grate cheese? Thin slices work in a pinch but won’t melt the same.

✔Storage Tips

Leftovers keep in an airtight container in the fridge for 3–4 days. Reheat gently covered in the oven or microwave; the sauce firms up when cold but comes back to life when warmed. Cold is fine for a cheeky breakfast the next day — pair it with a fried egg and pretend it’s intentional brunch.

✔Variations and Substitutions

If you’re dairy-free, try coconut cream (yes, it’s different, but still comforting) and a dairy-free cheese that melts reasonably well. For a smoky note, add a little smoked paprika or swap half the cheddar for smoked gouda. Short on time? Mix in some leftover roasted veggies between the layers for a heartier dish. Avoid using waxy potatoes unless you want a firmer bite.

Frequently Asked Questions

Caramelized Onion Scalloped Potatoes

Thin-sliced potatoes bake in a creamy onion sauce with melty Gruyère and Parmesan. Comforting, golden, and irresistibly savory.

Rate This Yum Pin This Recipe For Later! Share The Yum On Facebook Print

Prep Time: 30 minutes minutes

Cook Time: 1 hour hour 15 minutes minutes

Total Time: 1 hour hour 45 minutes minutes

Servings: 8

Ingredients

 

1x2x3x

Main Ingredients

• ▢ 2.25 lb Yukon Gold potatoes, thinly sliced Peeling optional
• ▢ 1.5 lb yellow onions, thinly sliced
• ▢ 3.5 tbsp unsalted butter for caramelizing onions
• ▢ 1 tbsp olive oil
• ▢ 2 tsp minced garlic
• ▢ 1.25 tsp fresh thyme leaves, chopped
• ▢ 2.5 tbsp all-purpose flour
• ▢ 1.5 cup heavy cream
• ▢ 1 cup whole milk
• ▢ 0.5 cup low-sodium chicken broth or vegetable broth
• ▢ 1 tsp Dijon mustard
• ▢ 2.25 cup Gruyère cheese, shredded
• ▢ 0.5 cup Parmesan cheese, finely grated
• ▢ 1.5 tsp kosher salt divided
• ▢ 1 tsp black pepper, freshly ground divided
• ▢ 0.25 tsp ground nutmeg
• ▢ 1 tbsp unsalted butter, for greasing for the baking dish
• ▢ 2 tbsp chives, finely chopped for garnish

Instructions

Preparation Steps

• Heat oven to 375°F. Butter a 9x13-inch baking dish.
• Caramelize onions: Warm butter and oil in a large skillet over medium-low heat. Add onions and 1/2 tsp salt. Cook, stirring often, until deep golden, 25–30 minutes.
• Stir in garlic and thyme; cook 1 minute until fragrant.
• Make the sauce: Sprinkle flour over onions and stir 1 minute. Whisk in broth, milk, and cream until smooth. Add Dijon, nutmeg, 1 tsp salt, and 3/4 tsp pepper. Simmer 3–4 minutes to slightly thicken. Remove from heat.
• Slice potatoes thinly if not done. Pat dry. Season with a pinch of salt and pepper.
• Layer half the potatoes in the dish, overlapping. Spoon half the onion cream over. Scatter one-third of the Gruyère and a little Parmesan.
• Repeat with remaining potatoes, sauce, and most of the remaining cheeses. Finish with the last handful of Gruyère and all the Parmesan on top.
• Cover tightly with foil and bake 45 minutes, until the potatoes are nearly tender.
• Uncover and bake 20–30 minutes more, until bubbling and deeply golden. Rest 10–15 minutes. Sprinkle with chives and serve.

Notes

Swap Gruyère with sharp white cheddar for a bolder bite, or add crisp bacon between layers for a smoky twist. Leftovers reheat well: cover and warm at 350°F until hot, or microwave individual portions. For extra browning, broil 1–2 minutes at the end.

This recipe is an original creation inspired by classic Caramelized Onion Scalloped Potatoes flavors. All ingredient ratios and instructions are independently developed.