For the béchamel sauce:
Melt the butter in a medium pot over medium heat. Add the flour and use a hand mixer to stir constantly until everything is well incorporated. The mixture will look a bit pasty. Continue stirring while adding the milk little by little. Season with salt, pepper and nutmeg. Reduce the heat to low and keep stirring. The mixture will begin to thicken. After the first boil let cook for 3-4 minutes. Remove from the stove and set aside.