Preheat oven to 350°F. in a medium saucepan melt butter add milk and 2 tablespoons taco seasoning. remove from heat and add potato flakes until incorporated. press mixture into the bottom of a 10 inch pan. Bake for 7 to 10 minutes until just barely turns golden brown. in a medium skillet cook beef and onions until beef is browned and cooked through. drain add salsa and remaining taco seasoning. cook until bubbly, pour into crust bake for 15 minutes or until crusts is golden brown. let cool for 5 minutes top with cheese lettuce and tomatoes cut and serve with sour cream