Do not be deterred by the word "croissant". Fear not, these are made with purchased puff pastry and come together faster than you can say "breakfast". Please note that you should refrigerate the dulce de leche for at least 24 hours before making these.
Preheat oven to 400 degrees.
Line a cookie sheet with parchment paper or you can use a Silpat. Divide the chocolate chips into 16 piles on your counter. You will use one pile for each croissant.
Put a little flour on a wooden cutting board or on a floured counter. Roll one sheet of pastry gently with a floured rolling pin. Do not press the dough down. The pastry sheet should look square about 10 inches on each side. Keep the other pastry sheet refrigerated and covered.
Cut the pastry into 8 pieces by first cutting it into four squares and then cutting each square in half diagonally until you have 8 triangles. You will make the remaining 8 croissants while the first ones are baking so the dough will stay cold.
Spread about 1/2 T. of very cold dulce de leche all each triangle and sprinkle with one of the piles of chocolate chips, stopping two inches before you get to the top and bottom edge of the triangle. Begin rolling each croissant very lightly into a roll starting at the wide end. You want to have a very light touch when you do this as you don't want to press the pastry down and you don't want too tight a roll. Gently pinch the sides closed.
When all 8 croissants are done, put them on the lined cookie sheet and put them in the refrigerator for at least 15 minutes and up to a half hour, covered with plastic wrap. Remove them and brush them lightly with the egg wash and sprinkle each one with a little bit of sugar.
Bake for 10 minutes. By this time some of the dulce de leche will have leaked out from the croissants to remove them from the oven and with a knife (I used a butter knife) scrape the dulce de leche back around the pastry like a little cozy cocoon. It will be thick and gooey and form a really nice glaze around each pastry. Bake for another 10 minutes. Watch carefully so the tops do not burn. Remove from the oven and let the croissants sit for 10 minutes to allow the filling to set. While the first batch is in the oven, repeat the process with the second pastry sheet. Serve warm or reheat in a preheated 400 degree oven for 5 minutes to puff them up a bit.