Line the 2 baking sheets with parchment paper.
Roll out 1 package of puff pastry on a floured surface to a 16" x 12" rectangle.
2 puff pastry sheets (1 package), 1 Tb. All-purpose flour (for surface)
Transfer to the parchment-lined baking sheet and chill while you roll out the remaining sheet of puff pastry.
Transfer to another parchment-lined baking sheet and chill both sheets of pastry until cold, about 15 minutes.
Transfer parchment paper with pastry to a clean surface and spread ¼ cup of mustard evenly over 1 sheet of pastry, leaving a ½" border around the edges.
¼ cup Buzz Savories Honey Mustard
If mustard is too thick for easy spreading, dilute with a tsp. of water or cream.
Layer ham, then cheese over the mustard.
8 oz cooked ham, thin sliced, 4 oz. Swiss cheese, thin sliced
Fold the border of pastry up over edge of filling and brush edges lightly with water.
Arrange remaining sheet of pastry on top, then trim edges with kitchen shears or a sharp knife so top layer fits over bottom with no overhang.
Crimp edges with a fork.
Using parchment, slide pastry back onto baking sheet. Chill, uncovered, at least 30 minutes.
Preheat oven to 400 Degrees.
Lightly beat egg and cream in a small bowl to blend. Brush egg wash evenly over puff pastry.
1 large egg, 1 tsp. heavy cream
Cut thin slits in a decorative pattern into top of pastry to allow steam to escape.
Bake feuillete, rotating pan halfway through, until puffed and deep golden brown, 30-35 minutes.
Let cool slightly before cutting into 1½" squares. Serve warm with additional mustard alongside.
Do Ahead: Feuillete' can be assembled 12 hours ahead. Cover with plastic wrap and keep chilled.