recipe scalloped potatoes

Ingredients 4 large russet potatoes, peeled and thinly sliced 2 tablespoons unsalted butter 1 small onion, finely chopped 2 cloves garlic, minced 2 tablespoons all-purpose flour 1 1/2 cups milk (whole or 2%) 1 cup heavy cream 1 teaspoon salt 1/2 teaspoon black pepper 1/4 teaspoon ground nutmeg (optional)