Heat oven to 400. Spray pie plate, 10x1.5", with Pam or other cooking spray. Mix leeks and 2c cheese in plate. Beat milk, eggs, Bisquick, salt and pepper until smooth. Pour into plate over leeks and cheese. Bake until knife inserted in center comes out clean, 25-35 min. Top with remaining cheese and bake 1-2 min longer until cheese is lightly browned. Let stand 5 min before serving. Garnish with tomato slices if desired.
Variations:
Replace leeks with: