Step 1 Spray an 11x8-inch tart pan with removable bottom with nonstick spray (you can also use a round 9-inch tart pan with removable bottom).
Step 2 Pulse together the flour, sugar and salt in a food processor several times to combine. Add the butter and pulse until fine crumbs form, about 15 seconds. Add the egg yolk, water and hazelnuts and pulse just to combine. The mixture should hold its shape when squeezed between your fingers. If it's too dry and crumbly, add another tablespoon of water. (Alternately, place the dry ingredients in a bowl and cut in the butter with two knives or a pastry blender until crumbs form. Stir in the egg yolk, water and hazelnuts.)
Step 3Place a piece of plastic wrap on a work surface. Form the dough into a small rectangle and seal tightly in the plastic. Refrigerate 1 hour. (If using a round pan, form dough into a circle.)
Step 4Roll out the dough between 2 sheets of plastic wrap to one-eighth-inch thickness. Place in the tart pan, pressing to fill the bottom and up the sides. Refrigerate 20 minutes. Prick the bottom with a fork, then bake until the bottom feels firm and the tart is pale golden, 17 to 20 minutes. Remove from the oven and cool completely.