Fill a deep, wide pot halfway with neutral flavored oil and heat to 350 degrees F.
Place the croissant dough on a gel board or over bench flour to keep from sticking.
Cut out doughnut shapes using the round cutters. Keep the dough from the holes and scraps, you can fry these too.
Refrigerate the dough for 10 to 15 minutes so that it is firmer and easier to work with.
Gently drop the chilled fro cro-doughs and scraps into the hot oil, making sure that you don't crowd the pot. Fry until cooked through and golden, 3 to 4 minutes per side. The scraps will take less time.
Once the doughnuts are cooked, place them on a paper-towel-lined plate to drain the oil. Allow to cool. Then dip the top part in the glaze.
Place the thin pastry tip in a plastic or pastry bag. Then fill with pastry cream and snip the tip with some scissors. Fill the fro cro-dough's with pastry cream in 3 spots, rotating to get an even fill. Glaze and fill the scraps as desired.