It only takes three simple steps to make the rich sauce for this melt-in-your-mouth mainstay.
Preheat oven to 400°. Microwave 2 cups milk at HIGH for 1 1/2 minutes. Melt 2 Tbsp. butter in a large skillet or Dutch oven over medium-low heat; whisk in 2 Tbsp. all-purpose flour until smooth. Cook, whisking constantly, 1 minute.