- 2 tablespoons butter
- 2 tablespoons flour
- 3 cups whole milk
- 1 teaspoon salt
- 1/4 teaspoon pepper
- 1/2 teaspoon garlic powder
- 1/4 teaspoon nutmeg
- 1/4 teaspoon dried thyme
- 2 cups Swiss cheese, shredded
- 2 pounds Russet potatoes, washed, peeled, thinly sliced
- 1 cup sweet onion, peeled, thinly sliced
- Preheat oven to 350°F.
- Coat a 9-inch pie plate or a small casserole dish with cooking spray.
- In a small sauce pan, melt butter over medium heat; add flour, whisking for 2 to 3 minutes or until incorporated.
- Gradually add milk, stirring until smooth.
- Add salt, pepper, garlic powder, nutmeg, and thyme; bring to a boil over medium-high heat, then lower to medium-low heat.
- Simmer for 5 to 7 minutes or until sauce is thickened.
- Add 1-1/2 cups of shredded Swiss cheese, stirring until cheese is melted; cook for an additional 3 to 5 minutes over medium-low heat until sauce is smooth.
- In a large bowl, combine potatoes and onions; add cheese sauce and toss to coat.
- Transfer potato mixture to prepared pie plate; wrap tightly with foil.
- Bake for 45 to 50 minutes or until potatoes are tender; remove foil.
- Top with remaining 1/2 cup of shredded Swiss cheese; bake, uncovered, for an additional 5 to 10 minutes or until cheese is melted and lightly browned.
Tip: Gratin can be prepared up to one day in advance, and reheated prior to serving.