Cheesy scalloped potatoes

Ingredients

• Potatoes: 3 lbs (about 5-6 medium) Russet or Yukon Gold potatoes, peeled and sliced 1/8-inch thick
• Butter: 1/4 cup (1/2 stick) unsalted butter
• Aromatics: 3 cloves garlic, minced, and 1 small yellow onion, finely diced
• Flour: 1/4 cup all-purpose flour (to thicken the sauce)
• Dairy: 2 cups heavy cream (or half-and-half) and 1 cup whole milk
• Cheese: 3 cups freshly grated sharp cheddar cheese and/or Gruyère cheese (divided)
• Seasoning: 1 teaspoon salt, 1/2 teaspoon black pepper, 1/4 teaspoon ground nutmeg, and a pinch of smoked paprika (optional)
• Fresh Herbs: Chopped fresh parsley or chives for garnish

Step-by-Step Instructions

1. Prep Oven and Baking Dish: Preheat your oven to 190°C (375°F). Lightly grease a 9×13-inch baking dish with butter or cooking spray.
2. Make the Cheese Sauce (Mornay):
   • Melt the butter in a large saucepan or Dutch oven over medium heat. Add the diced onions and cook for 3-4 minutes until translucent. Add the minced garlic and cook for 1 more minute until fragrant.
   • Whisk in the flour and cook for 1 minute to remove the raw flour taste.
   • Slowly pour in the heavy cream and milk while whisking constantly to prevent lumps. Bring to a gentle simmer, stirring frequently, until the mixture thickens.
   • Remove from heat and stir in 2 cups of the grated cheese, salt, black pepper, and nutmeg until completely melted and smooth.
3. Layer the Potatoes: Arrange half of the sliced potatoes in an even overlapping layer in the bottom of your prepared baking dish. Pour half of the warm cheese sauce evenly over them. Repeat with the remaining potatoes and the rest of the cheese sauce.
4. Bake Covered: Cover the baking dish tightly with aluminum foil. Bake at 190°C (375°F) for 45 minutes. (Covering traps steam so the potatoes cook all the way through without burning the top).
5. Brown the Top: Remove the foil, sprinkle the remaining 1 cup of cheese (and a pinch of paprika) over the top, and bake uncovered for another 25 to 30 minutes, or until the potatoes are fork-tender and the cheese on top is deeply golden, bubbling, and crisp.
6. Rest Before Serving: Let the casserole rest for 15 to 20 minutes before slicing and serving. This crucial step allows the rich cream sauce to set so your slices hold their shape.

Pro-Tips for Success

• Slice Evenly: Use a mandoline slicer if you have one to ensure all potato slices are the exact same thickness (about 1/8 inch), which guarantees they cook evenly.
• Grate Your Own Cheese: Pre-bagged shredded cheese is coated with anti-caking starches that prevent it from melting smoothly into a creamy sauce. Freshly grated cheese makes a massive difference!
• Potato Choice: Yukon Golds give a buttery flavor and slightly creamier texture, while Russets release more starch, which naturally helps thicken the sauce even further.

Note: If you want to prep ahead, you can assemble the entire casserole a day in advance, keep it covered in the refrigerator, and just add an extra 15 minutes of covered baking time when you’re ready to cook it.