|¼ cup (56g)||Plugrá® Premium Butter, salted|
|⅓ cup (50g)||finely chopped onion|
|¼ cup (33g)||all-purpose flour|
|½ tsp. (3g)||salt|
|¼ tsp. (.25g)||ground white pepper|
|⅛ tsp. (.25g)||ground nutmeg|
|3 cups (732g)||milk|
|1¼ cups (141g)||shredded Parmesan cheese|
|3 pounds (1.36kg)||russet potatoes, peeled and cut into thin slices|
Heat oven to 350°F. Spray a 13 x 9-inch pan with non-stick cooking spray.
Melt the butter in a medium saucepan over medium heat. Add the onion and cook stirring occasionally for about 2 minutes or until the onions are tender. Stir in the flour, salt, pepper and nutmeg. Reduce heat to low and cook, stirring constantly, for 2 minutes.
Increase heat to medium and whisk in about ¼ cup of milk, making sure it is fully blended and there are no lumps. Whisk in the remaining milk about ¼ cup at a time until the mixture is thin and smooth then add the remaining milk, being sure to mix well to avoid any lumps. Heat to boiling, stirring constantly. Boil and stir 1 minute. Add the cheese and stir until it is fully melted. Remove from heat; set aside.
Layer the potatoes in the prepared pan. Pour sauce over potatoes. Cover with buttered aluminum foil and bake for 45 minutes. Uncover; bake 30 to 40 minutes longer or until potatoes are tender and the top has browned. Let stand 5 to 10 minutes before serving to allow the sauce to thicken.