At least 4 hours before cooking, trim crusts and cut bread into 1" squares. Cut cheese into bite size pieces. In large greased casserole, alternate layers of bread and cheese. Pour melted butter over top. Beat eggs well, stir in salt, pepper, mustard and milk. Combine thoroughly. Pour over casserole. Cover and refrigerate. One hour before serving, bake at 350 degrees, 30 minutes covered, then 30 minutes uncovered until top is golden and puffy.