Preheat your oven to 400 degrees.
Place the puff pastry sheets on your work surface so the longest edge faces you. Using a pastry brush cover each sheet of puff pastry with a thin coating of Dijon mustard. Add a single layer of proscuitto, leaving a 1" margin at the edge farthest from you. Sprinkle with cheese. Gently and tightly roll up the works. With your sharpest knife, slice the 'log' into 1/2 to 1 inch thick rounds and lay on a parchment or silicon lined baking sheet. The slices may deform a bit, reform with your fingers and don’t worry: they’ll look great when they bake! Leave some expansion space between the pieces. Bake for 10-15 minutes, until puffed and golden brown.
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