Chop spinach; add salt, pepper, butter, beaten egg yolks, and cream. Beat whites until frothy, add baking powder and beat stiff. Fold into mixture. Bake in buttered casserole 50 minutes at 350°.
NOTES : Broccoli may be substituted for spinach. If so, add 1 tablespoon lemon juice, some sharp cheese and minced garlic.