Cook macaroni in medium saucepan for 8 to 10 minutes or until almost tender; drain. Return macaroni to saucepan. Add butter; stir until melted.
Whisk together evaporated milk, eggs, mustard and pepper in medium bowl. Add to macaroni mixture along with cheese; stir. Cook over low heat, stirring constantly, until cheese begins to melt. Pour into 1 1/2-quart casserole dish.
Bake for 10 minutes; stir. Bake for an additional 20 to 25 minutes or until bubbly and top is lightly golden. Season with salt.
FOR FREEZE AHEAD:.
Prepare as above; do not bake. Cover; freeze up to 2 months. Thaw overnight in refrigerator.