Preheat your oven to 350˚F. Line a baking tray with silpat or parchment paper.
Roll out your puff pastry to a 10×12 inch rectangle. Using a 3-inch round cutter, cut out 12 circles from the pastry.
Cut the ham slices into squares about 1 1/2 inches in size.
Take a small piece of ham and place it in the center of a puff pastry circle. Top with a pinch of the grated cheese. Using a pastry brush, brush some beaten egg around the edges of the pastry circle. Fold over so you have a half moon and press the edges together. Place on your baking tray and using the tines of a fork, press on the seam to ensure the pastry will not come apart when baking. Repeat with the rest of the pastry rounds.
Brush the top of each ham and cheese crescent with the beaten egg and sprinkle some sesame seeds on top. Bake in the oven for 12-15 minutes. The pastry should turn a nice golden brown color on top.
While the crescents are in the oven, combine the dijon mustard and mayonnaise in a small bowl. Voilà, you have dijonnaise. Serve alongside the crescents.