Potatoes and Leeks Au Gratin

Heat oven to 350ºF.

In a large skillet over medium heat, melt 3 tablespoons butter. Add flour and whisk until smooth. Stir in 1 teaspoon salt and pepper. Add milk gradually, whisking well after each addition. Remove from heat.

Add 1/2 cup each cheddar and Parmesan cheeses. Stir until melted.

Grease a 2-quart baking dish (I sprayed with nonstick spray). Layer potatoes and leeks in two layers, topping each with about 1/3 of the sauce. Top with remaining potatoes, leeks, and sauce. Dot with remaining 1 tablespoon butter.

Cover and bake for about 45 minutes. Uncover and bake 45–55 minutes longer, until potatoes are tender. During the last 5 minutes of bake time, sprinkle the remaining cheeses on top.

Let set about 10 minutes and serve.