Baked Brunch Sandwiches

This recipe is from Taste of Home website. I made these for my son's baptism and they were easy and a big hit.
3 Tbsp. Dijon mustard
12 slices bread
6 slices fully cooked ham
12 slices cheddar or swiss cheese (I used cheddar)
1 medium tomato, thinly sliced
3 Tbsp. butter, softened
4 eggs
1/4 c. milk
1/4 tsp. pepper

Spread mustard on one side of six slices of bread. Layer the ham, cheese, and tomato over the mustard; top with remaining bread. Butter the outsides of the sandwiches; cut in half. Arrange in a greased 13-in. x 9-in. x 2-in. baking dish.
In a small bowl, whisk the eggs, milk and pepper; pour over sandwiches. Cover and refrigerate overnight.
Remove from the refrigerator 30 minutes before baking. Bake, uncovered, at 375 for 30 minutes or until a knife inserted in the center comes out clean.