Impossible Broccoli Pie--It's impossible that it is this easy and this delicious!

20 oz. frozen chopped broccoli (or fresh broccoli)
3 c. shredded cheddar cheese, divided
2/3 c. chopped sauted onion
1 1/2 c. milk
3 eggs
3/4 c. buttermilk baking mix
3/4 t. salt
1/4 t. pepper

Rinse broccoli under cold water to thaw and drain. Saute or microwave onions. Mix broccoli, 2 cups of cheese and onion in greased pie plate or 9x9 in. baking dish. Beat milk, eggs, baking mix, salt and pepper until smooth. Pour into dish. Bake at 400* for 25-35 minutes or until knife inserted comes out clean. Top with remaining 1 cup of cheese. Bake until cheese is melted. Serves six.