Heat oven to 375. Spray 2 muffin pans with cooking spray.
In skillet, cook sausage and onion over medium high heat 5 to 7 minutes, stirring frequently, until sausage is no longer pink; drain. Cool 5 minutes; stir in mushrooms, salt, sage and cheese.
In medium bowl, stir baking mixture ingredients with whisk or fork until blended. Spoon 1 scant tablespoon baking mixture in to each muffin cup. Top with about 1/4 cup sausage mixture. Spoon 1 tablespoon baking mixture onto sausage mixture in each muffin cup.
Bake about 30 minutes or until toothpick inserted in center comes out clean, and tops of muffins are golden brown. Cool 5 minutes. With thin knife, loosen sides of pies from pan; remove from pan and place top sides up on cooling rack. Cool 10 minutes longer, and serve.