01 -
Preheat your oven to 400 degrees F. Butter a 9x13-inch baking dish.
02 -
Arrange the peeled and sliced potatoes in about three layers in the baking dish.
03 -
In a 5-quart saucepan, melt the butter over medium heat.
04 -
Add onion and garlic, cooking until the onion becomes soft, approximately 5 minutes.
05 -
Stir in the flour, salt, and pepper, cooking for about 1 minute until the roux just begins to brown.
06 -
Whisk in milk and heavy cream, cooking over medium heat until thickened, about 1-2 minutes. Taste and adjust salt and pepper as desired.
07 -
Pour the sauce over the potatoes in the baking dish.
08 -
Cover and bake in the preheated oven for 30 minutes.
09 -
Remove the foil and continue baking for an additional 30-45 minutes until the potatoes are soft and the top is lightly browned.