Place the ground beef and onion in a large skillet over medium high heat. Saute for 5 to 10 minutes, or until beef is browned and onion is translucent; set aside.Advertisement
Melt the butter or margarine in a medium saucepan over medium heat. Remove from heat and add the flour, mixing thoroughly.
Add the milk slowly, stirring constantly, and return to the heat. Keep stirring until thickened to desired consistency.
Add the reserved beef mixture, the peas, and season with salt and pepper to taste.