To make the pastry dough, combine the flour, sugar, and salt in a food processor and pulse to blend. Add the butter and pulse until the mixture has a sandy texture. Add the egg yolks and pulse twice, then add the water and vanilla and pulse a few times to incorporate. Pinch a bit of the dough between your fingers; it should hold its shape without feeling dry. If needed, add another teaspoon or two of water. Turn the dough out onto the work surface and form into a disk. Wrap in plastic and refrigerate for at least 30 minutes.
Preheat the oven to 375°F. Line 2 baking sheets with silicone baking mats or parchment paper. Set 2 oven racks on the centermost levels.
Roll the dough out on a lightly floured surface to a circle about 14 inches across and ⅛ inch thick (let the dough sit for 10 or 15 minutes if it is too firm to roll right away). Use a 2¾-inch round cutter (plain or fluted) to cut rounds from the dough. Arrange them about 1 inch apart on the baking sheets. Bake until lightly browned, about 15 minutes, switching the pans about halfway through for even cooking. Let cool slightly on the baking sheets, then transfer the pastry to a wire rack to fully cool.
Cut the banana into ¼ inch slices and put them in a bowl with the orange juice. Toss gently to be sure that all slices are fully coated in the juice and let sit a few minutes. Transfer the slices to a piece of paper towel and lightly pat the tops to dry. Top each pastry round with 1 teaspoon of the Nutella and spread it out a bit, leaving a ½-inch border. Arrange 2 or 3 banana slices, slightly overlapping, on top of the Nutella. Sprinkle the bananas with chopped hazelnuts and arrange on a platter for serving.