Magic Spinach and Egg Bars, from Sarah

10 oz chopped, frozen spinach, thawed and drained
4 T butter
3 eggs beaten
1 C milk (whole)
3/4 C flour
1 tsp salt
1 tsp baking powder
12-16 oz grated sharp cheese (I use shredded and it's fine)
1 small onion chopped (I skip this and use onion powder)
1/2 C fresh chopped mushrooms (also optional)

Preheat oven to 350*
melt butter in 13x9 pan or something close
beat eggs, milk, flour & baking powder
Combine remaining ingredients and spoon into pan
Bake at 350* for 35 minutes or until lightly browned
Cut into squares and eat hot or cold