Preheat oven to 350° F.
Combine milk, biscuit mix, butter, eggs and salt in blender and mix well. Turn into ungreased deep dish 9-inch pie plate.
Add meat, shellfish or vegetables, poking into batter. Top with onions, mushrooms, and cheese.
Bake until top is golden, about 45 minutes. Let stand 10 minutes before serving.Makes 6