First, preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper. This will prevent the croissants from sticking.

Gently unfold the thawed puff pastry on a lightly floured surface. If your puff pastry comes in two sheets, that's perfect. If it's one large sheet, you may want to cut it in half to make it easier to work with.

Using a rolling pin, lightly roll out the pastry to smooth out any creases and make it slightly thinner.

Spread a thin, even layer of Nutella over one sheet of the puff pastry, leaving about a half-inch border around the edges.

Arrange the sliced strawberries evenly over the Nutella.

Carefully place the second sheet of puff pastry on top (if your pastry came in two sheets). If you had one large sheet and cut it, now's the time to place the second half on top.

Using a sharp knife or a pizza cutter, cut the pastry into triangles. You can make them as big or as small as you like, but I find that triangles about 4-5 inches wide at the base work well.

Starting at the wide end of each triangle, gently roll it up towards the point. Place the rolled croissants onto the prepared baking sheet, making sure the point is tucked underneath to prevent it from unrolling during baking.

Brush the tops of the croissants with the beaten egg. This will give them a beautiful golden-brown color and a slight sheen.

If you like, sprinkle a little coarse sugar over the egg-washed croissants for added sweetness and a bit of crunch.

Bake for 15-20 minutes, or until the croissants are puffed up and golden brown. Keep an eye on them, as ovens can vary.

Let the croissants cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely (or enjoy them warm!).