1 (10 oz.) pkg. sharp Cheddar cheese, grated
2 (10 oz.) pkgs. frozen, chopped spinach, thawed and squeezed dry
2/3 c. chopped onion
18 thin slices white bread, trimmed (I use about 12)
1/2 c. butter, softened (to spread on bread slices)
4 eggs
4 c. milk
1 tbsp. prepared mustard
2 tsp. salt
1/4 tsp. pepper

Spread bread slices on both sides with softened butter; place slices on bottom of greased baking dish (13 x 9 x 1 3/4); cut to fit dish. Toss together 2 cups cheese, spinach, and onion. Top bread slices with 1/2 of cheese and spinach mix. Add more bread slices and more of cheese mix.

Cut remaining bread into quarters and arrange on top of casserole. Top with remaining shredded cheese. Beat together milk, eggs, mustard, and seasoning; pour carefully over casserole; cover and refrigerate at least 1 hour or overnight.

Bake at 350 degrees about 60-65 minutes or until knife inserted in center comes out clean. Let stand for 15 minutes before cutting into squares. Makes 8-10 servings. Great to make ahead for busy bodies.