Low Carb, Gluten Free Musroom-Onion Quiche

1/2 cup onion, sliced very thin
2 cups sliced mushrooms
1 T. Butter
6 eggs
1 cup 1% milk
2 cups shredded cheddar cheese
1 t salt
1/4 t baking powder
1/2 t pepper
1/4 t nutmeg
1 t basil
1/4 cup soy flour

Preheat oven to 350F. In a skillet, melt butter, and saute mushrooms and onions until onions are translucent and tender. Place onions and mushrooms in a 9 inch skillet. Add cheddar cheese. Mix together eggs, milk, salt, pepper, nutmeg, basil, soy flour and baking powder, and pour over mushrooms, onions, and cheese. Bake for 40 minutes until browned around the edges, and the center is firm.