Preheat oven to 375°F (190°C)
Butter a baking dish (about 2–3 quarts)
Thinly slice 2–3 pounds of potatoes (about 1/8 inch thick); keep slices uniform
In a bowl, mix 2 cups milk (or half-and-half), 1 to 2 cups shredded cheese (optional), 1 teaspoon salt, 1/2 teaspoon black pepper, 1/4 teaspoon garlic powder, and 1/4 teaspoon paprika (optional)
In the baking dish, layer potatoes and pour/spoon sauce over each layer
Dot the top with 2–4 tablespoons butter (optional)
Cover with foil
Bake 45–60 minutes, until potatoes are tender when pierced with a knife
Uncover and bake 10–20 minutes, until top is golden and bubbling
Rest 5–10 minutes before serving