How to Make It
Cook the pasta according to the package directions.
Wipe out the pot and melt the butter over medium heat.
Add the flour and cook, stirring constantly, for 2 minutes. Slowly add the milk while stirring. Cook, stirring occasionally, until the sauce slightly thickens, 6 to 8 minutes. Add the Cheddar-Jack, mustard, and pepper and stir to melt. Stir in the pasta.
Transfer to a 9-by-13-inch (3-quart) baking dish and cover with the Muenster. Cool completely. Cover tightly with plastic wrap and refrigerate until ready to bake, up to 4 days.
To cook: Bring to room temperature. Bake at 400° F until golden and warmed through, 25 to 35 minutes.