A twist on the classic French Croque Madame. This delicious sandwich features layers of savory ham, melted Gruyère cheese, and a creamy béchamel sauce, topped with a perfectly cooked egg.
Preheat Oven: Set your oven to 375°F with a rack in the center position.
Béchamel Sauce: In a medium skillet, melt butter over medium heat. Add the flour, whisking for about 30 seconds. Gradually add milk, whisking until smooth. Cook until the sauce thickens (about 4 minutes). Remove from heat and stir in mustard, salt, and nutmeg.
Prepare Sandwiches: Spread butter on one side of each bread slice. Place four slices, buttered side down, on a baking sheet. Add ham and cheese on each. Top with remaining bread slices, buttered side up. Bake for about 6 minutes, or until the bread is golden and cheese melts.
Broil: Spread béchamel sauce over sandwiches. Add extra cheese if desired. Broil until cheese bubbles and browns (3-4 minutes).
Fry Eggs: In a skillet, heat a bit of butter or oil. Fry eggs until whites are set but yolks are still runny (about 5 minutes). Place an egg on top of each sandwich.
Serve: Garnish with chives, microgreens, and black pepper. Serve immediately.