Arrange racks in center and lower third of oven; preheat to 400°. On a lightly floured surface, roll out 1 pastry sheet to a 10" square. Brush off excess flour. Spread half of Nutella over pastry, leaving a ½" border at the top and bottom.
Cut dough in half crosswise, then cut lengthwise into 2"-wide strips. You should have 10 (5" x 2") strips.
Using a pastry brush, brush exposed edges with egg wash. Starting at a short end, roll each strip into a tight log. Arrange seam side down on a parchment-lined baking sheet. Lightly brush tops with egg wash. Repeat with second pastry sheet and another parchment-lined baking sheet.
Bake pastries, rotating sheets top to bottom halfway through, until puffed and deeply golden, 20 to 25 minutes. Transfer to a wire rack and let cool 15 minutes.
Dust with confectioners’ sugar (if using) before serving.
