Whisk the milk and eggs together in a small mixing bowl and pour into a rectangular casserole. Spread one side of each piece of the bread with mustard. Place all the slices in a single layer mustard side up so they can soak up the milk mixture.
Layer half of the slices with cheese, then ham, then more cheese. Take the remaining slices and lay them wet side UP on top of the sandwich bottoms (in other words, both outside bread slices are the ones that are wet with the milk mixture).
Put the butter in a large skillet or a griddle over medium heat. Carefully place the sandwiches in the skillet or on the griddle and cook until the bottom of the sandwich is golden brown about 3 minutes.
Carefully turn the sandwiches over and cook for another 3 minutes or until the other side is golden brown.
It’s going to be tempting to dig into these RIGHT AWAY, but it’s best if you let them cool for a minute or two before you take that first bite!
Notes
Bread: We recommend the softest bread you can find (regular sandwich bread is a-ok) so that it soaks up all the egg mixture.
Ham: We usually use thin sliced ham for this recipe, but if you have thicker ham slices those will also work just fine.
Cheese: Not a Swiss cheese fan? American, Cheddar and Muenster are also delicious in this sandwich.