Preheat Oven: Set your oven to 375°F.
Prepare Puff Pastry: Thaw the puff pastry sheet by leaving it at room temperature for 1 hour. Alternatively, wrap it in paper towels and microwave for 15 seconds on each side until soft enough to unfold.
Cut the Pastry: Unfold the pastry sheet and cut it into 9 squares. For larger pinwheels, cut into 4 or 6 squares.
Create Center Circles: Draw a circle in the center of each square without cutting through, using a cookie cutter or glass rim.
Make Slits: Use a sharp knife to cut slits from the outer edge of the circle to the corners, leaving the center intact for filling.
Add Filling: Place 1-2 teaspoons of your chosen filling in the center of each square. Add a dollop of Nutella, cheesecake filling, cookie butter, dulce de leche, or a piece of chocolate.
Add Berries: Place four berries at the tips of each triangle around the filling.
Fold Corners: Fold every other corner towards the center. Start with one corner, skip the next, and continue folding until all four corners are folded in. Place another berry in the center to secure the folds.
Brush with Egg Wash: Whisk the egg and brush it over the pastry. Sprinkle with coarse sugar.
Bake: Bake for 15-20 minutes, until golden brown and puffed up. Adjust the baking time if making larger pinwheels.
Cool and Serve: Remove from the oven and let them cool briefly before serving.