SPRAY 5 full hotel pans (or 1 half hotel pan for trial recipe) with cooking spray. Trim crusts from bread slices; arrange slices evenly on bottoms of pans. Top evenly with half each of the of the process cheese, onions and broccoli. Repeat all layers.
BEAT egg product, milk and mustard in 3-gal. bowl (or 1-qt. bowl for trial recipe) with wire whisk until well blended. Pour evenly over ingredients in pans. Cover and refrigerate several hours or overnight.
BAKE, uncovered, in 275°F-convection oven for 1 hour to 1 hour and 20 minutes or until knife inserted in centers comes out clean. Let stand 5 minutes before cutting strata in each pan into 16 squares (or 8 squares for trial recipe) to serve.