Preheat the oven to 350┬░F. Butter a 2-quart gratin dish. Drop into a pot of boiling water for 5 minutes, then drain, rinse with cool water and pat dry:
3 pounds Yellow Finn potatoes or all-purpose potatoes, peeled and sliced into l/8-inch rounds
Layer a third of the potatoes in the gratin dish, followed by:
Salt and pepper
1/3 cup grated sharp Cheddar cheese or Gruyère cheese (optional)
2 tablespoons finely diced onion
1 teaspoon flour
Repeat the steps twice, then pour over:
2 cups milk or light cream, warmed
Cover with foil and bake for 45 minutes. Uncover and continue to bake until the potatoes are tender, most of the liquid is absorbed, and the top is golden brown, 15 to 30 minutes.
