traditional scalloped potatoes recipe

Ingredients: 2 pounds potatoes (Yukon Gold or Russet), peeled and thinly sliced 2 tablespoons butter 1 small onion, finely chopped 2 cloves garlic, minced 2 tablespoons all-purpose flour 1 1/2 cups milk 1/2 cup heavy cream 1 cup shredded cheddar cheese 1/2 teaspoon salt 1/4 teaspoon freshly ground black pepper