Preheat oven to 350 degrees.
Make a roux by melting butter in a saucepan. Add flour and whisk until smooth.
In a large bowl beat eggs, milk, baking powder, salt, sugar, and cream of tartar. Stir in cheddar and cream cheeses, green onions, and butter roux until blended.
Pour into two well-greased, 8x10 inch ceramic baking dishes. Bake uncovered 30 minutes.
Servings 12