Preparation

Step 1 out of 12

Preheat oven to 400 °F and grease a one-quart pan.

Step 2 out of 12

Finely slice potatoes to 1/8” thick.

Step 3 out of 12

In a medium saucepan, melt butter over medium-low heat. Add garlic and cook for one minute until fragrant.

Step 4 out of 12

Add flour and continue to whisk until completely combined with butter (leaving no lumps).

Step 5 out of 12

Slowly add milk, a few tablespoons at a time, whisking constantly, until milk has been added and no lumps of flour remain.

Step 6 out of 12

Whisking constantly, bring roux to a strong simmer (almost a boil), and reduce heat to medium-low.

Step 7 out of 12

Simmer until roux thickens, about 3 to 5 minutes (roux should be at a slow simmer over lower heat. The roux will break if the heat is set too high).

Step 8 out of 12

Add thyme, salt, pepper, and 1 1/2 cups cheddar cheese to roux and stir until well combined. Set roux aside.

Step 9 out of 12

Layer half the potatoes in buttered dish and top with chopped onion. Pour about 1/3 of the roux over onions and then layer remaining potatoes over top. Top with remaining sauce, remaining cheddar cheese, Parmesan cheese, and sprinkle paprika over top.

Step 10 out of 12

Spray one side of a piece of foil and cover (sprayed side down) prepared dish. Bake for 45 minutes.

Step 11 out of 12

Carefully remove foil and bake for 15 to 20 minutes more until top is golden brown.

Step 12 out of 12

Allow to cool for 5 to 10 minutes before serving.