Preheat oven to 400°F and generously grease a 9-inch pie plate with butter.
In a large skillet over medium-high heat, cook ground beef and chopped onion until beef is browned and onion is tender, about 8 minutes, then drain well.
Season the beef mixture with salt, pepper, and garlic powder, then spread evenly in the bottom of the greased pie plate.
Sprinkle shredded cheddar cheese over the beef mixture.
In a blender or mixing bowl, combine milk, Bisquick baking mix, and eggs, blending until smooth.
Pour the batter evenly over the beef and cheese in the pie plate.
Bake for 30-35 minutes until a knife inserted in the center comes out clean and the top is golden brown.
Let the pie stand for 5-10 minutes before slicing and serving.