Step 1

Preheat oven to 375°F.

Step 2

Melt butter over medium heat in a medium saucepan. Add onion and sauté for about 5-7 minutes until softened and lightly golden. Add garlic and thyme and stir for 30 seconds.

Step 3

Stir in 1 cup milk, salt, paprika, pepper, and nutmeg. Bring to a low boil, stirring constantly, and reduce heat to a simmer.

Step 4

Stir together remaining 1/4 cup milk and cornstarch, and add to the simmering milk. Simmer for another minute, stirring constantly, then remove from heat. Add in gruyere and stir until melted.

Step 5

Layer half of the sliced potatoes into an 8 inch square or circle baking dish. Pour half of the cheese-milk sauce over the potatoes. Top with the other half of the potatoes and pour the remaining cheese sauce on top. Sprinkle with mozzarella cheese, and cover with foil.

Step 6

Bake in preheated oven for 35 minutes. Remove foil and bake another 5-10 minutes until potatoes are done and cheese is bubbly. Let sit for about 10 minutes before serving. Enjoy!