Wash the broccoli and drain. Chop the broccoli into bite-sized pieces, separating the stalks from the florets.
Fill a medium-sized saucepan with 1 inch of water. Place a metal steamer inside the pan. Make sure the water is not touching the bottom of the steamer. Heat the water to boiling. When the water is boiling, add the broccoli to the steamer. Cover and steam until the broccoli is tender, about 10 minutes. Drain and set aside.
In a medium-sized saucepan, melt the butter over low heat. Stir in the flour. Cook for 2 minutes, stirring continually. Whisk in the milk, garlic powder, and salt and pepper. Bring to a boil over medium heat, whisking continually.
Reduce heat slightly and whisk in the cheese, and then the sour cream. Return to a boil and heat through. Arrange the broccoli on a plate and pour the cheese sauce over the top.
Sour cream adds rich flavor to this simple sauce. Steamed cauliflower or asparagus can be used in place of the broccoli.