Preheat oven to 400 degrees. Line 2 baking sheets with parchment paper. You don't have to do this, but it makes for easy cleanup.
Remove the puff pastry from the package. Roll one sheet out to about 2-3 inches larger than what it was originally.
Cut it into 9 squares. They don't need to be perfect, so don't stress.
Add a touch of mustard to the center of each square, then about 2 tablespoons chopped ham and 1-2 tablespoons grated cheese.
Mix your egg and milk together to make your egg wash. Brush 2 edges of the square, then fold it over to form a triangle.
Move it to the baking sheet and press the 2 open edges with a fork to ensure they stay closed.
Repeat with all the squares. When they are all done, brush the tops with egg wash and bake until they are golden brown.
They are best eaten fresh while it is still crispy and delicious.
Now, sit back and enjoy. You deserve it!