For a deeper hazelnut flavor, toast the hazelnuts before grinding. Toast them in a 350°F (175°C) oven for 8-10 minutes, or until fragrant. If the tart crust edges are browning too quickly during baking, cover them with aluminum foil. A dusting of powdered sugar adds a touch of elegance before serving. The tart is best enjoyed the day it is baked, but it can be stored in the refrigerator for up to 2 days.