Creamy, layered scalloped potatoes baked golden with a cheesy top are a comforting, vegetarian family holiday side. This rich, indulgent dish is a beloved addition to any dinner table.
Preheat oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish with butter for even browning.
Peel and slice potatoes thinly (about ⅛ inch thick) and soak in cold water for 10 minutes to remove excess starch. Drain well and pat dry to prevent watery sauce.
In a medium saucepan over medium heat, melt butter. Add sliced onions and sauté for 4–5 minutes until softened but not browned for gentle sweetness.
Sprinkle in the flour and cook, whisking constantly for 1–2 minutes to remove raw flavor. Gradually whisk in milk and cream, keeping heat medium to avoid scorching.
Add salt, pepper, and garlic powder. Simmer gently for 3–4 minutes until slightly thickened. Remove from heat and stir in 1 cup cheddar until melted.
Layer half of the potatoes in the baking dish, slightly overlapping the slices. Pour half the cheese sauce evenly over the top. Repeat with remaining potatoes and sauce.
Sprinkle the remaining ½ cup cheddar cheese over the top. Cover with foil (non-stick side down) and bake for 40 minutes.
Remove foil and bake an additional 20–25 minutes, until the top is golden and the potatoes are tender when pierced with a knife.
Let rest for 10 minutes before serving for the sauce to set, ensuring clean slices and best texture.