Ingredients

6 tablespoons butter (separated)

1 tablespoon olive oil

1 large yellow onion

½ teaspoon dried thyme

2 cloves garlic (minced)

4 tablespoons flour

3 cups milk

3 ½ cups shredded orange cheddar cheese (divided)

2 tablespoons cream cheese (softened)

½ teaspoon mustard powder

½ teaspoon salt

¼ teaspoon pepper

1 pinch cayenne pepper

2.5 lbs Yukon Gold or Russet potatoes (about 6 medium potatoes)

Instructions

Step 1: Preheat the oven to 350°F (175°C).

Step 2: While the onions caramelize, measure out the remaining ingredients.

Step 3: Cut the onion into ¼ inch thin strings. In a large skillet, melt 2 tablespoons butter with olive oil over medium-low heat. Add the onions and dried thyme. Cook slowly, stirring every few minutes, for about 30 minutes until the onions are brown and caramelized. Remove from heat and set aside.

Step 4: Increase heat to medium. Add 4 tablespoons butter and the minced garlic to the skillet. Cook for 1 minute, using a spatula to scrape the bottom and sides of the pan. Stir in the flour and whisk continuously for about 1 minute, until the raw flour smell is gone.

Step 5: Gradually pour in the milk in small splashes while whisking constantly to prevent lumps. Bring the mixture to a boil, then remove from heat.

Step 6: Stir in mustard powder, salt, pepper, and a pinch of cayenne pepper until combined.

Step 7: Let the sauce cool slightly. Reserve 1 heaping cup of shredded cheddar cheese. Gradually add the remaining cheese into the sauce, stirring gently to avoid separation.

Step 8: Mix in the softened cream cheese and then fold in the caramelized onions.

Step 9: Peel the potatoes, rinse, and pat dry. Slice them into thin, even pieces about 1/8 inch thick.

Step 10: Lightly grease a 9×13-inch baking dish. Arrange half the sliced potatoes in an even layer on the bottom. Pour half of the cheese sauce over the potatoes. Repeat with the remaining potatoes and cheese sauce. Sprinkle the reserved cheddar cheese evenly on top.

Step 11: Cover the dish and bake at 350°F for 45 minutes. Remove the cover and bake for an additional 40 minutes, or until potatoes are tender and cooked through.

Step 12: Optional: Broil on high (about 400°F) for a few minutes until the top is lightly browned and bubbly. Watch closely to prevent burning. Allow to sit for 5–10 minutes before serving. Garnish with fresh parsley if desired.

Tips & Variations

Use Yukon Gold potatoes for a creamier texture or Russets for a fluffier bite.

Caramelizing the onions slowly adds depth and sweetness—don’t rush this step.

Add a pinch of nutmeg to the cheese sauce for a subtle warm spice note.

Swap half the cheddar for Gruyère for a richer, nuttier flavor.

For a crispier top, sprinkle panko breadcrumbs mixed with melted butter before baking uncovered.

FAQs

Can I prepare scalloped potatoes ahead of time?

Yes, you can assemble the dish up to the baking step and refrigerate it covered overnight. Bake it longer if cold from the fridge, or allow it to come to room temperature before baking to ensure even cooking.

What is the difference between scalloped potatoes and au gratin potatoes?

Scalloped potatoes typically feature a creamy sauce without a breadcrumb topping, while au gratin potatoes include cheese and breadcrumbs on top for a crispy, browned crust.