Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper or a silpat or grease well.
Spread out the sheet of puff pastry on a clean work surface sprinkled with flour. Flatten it out with your hands or use a rolling pin to smooth it a bit.
Use a pizza cutter to cut the pastry into 3 strips (right along the fold lines). Make 4 cuts the other way, so you end up with 12 squares.
At this point you can add the nutella and bake, or if you want the baby ones that are shown in the final photos, split each square in half one more time to make a rectangle. Use two spoons to add a very small amount of nutella to the center of each piece of dough. Seriously, we're talking like a teaspoon at the most. (Add a little more if you are only making 12 puffs.)
Fold the dough over and seal by pinching them together with wet fingers. Have a bowl of water nearby to keep your fingers wet.
Place the sealed dough on the prepared baking sheet. Continue with the rest of the dough.
Bake 9-12 minutes, or until the tops are golden.