The entire recipe can be found here. The original recipe calls for 1/2 cup chopped toasted walnuts but I substituted 1/2 cup chopped toasted hazelnuts instead. You can use either nut, just make sure to toast and let cool completely before grinding in the food processor.
Dough in buttered tart pan.
In the bowl of an electric mixer fitted with the paddle attachment, beat the butter, sugar and vanilla until light and fluffy. Add the flour mixture and mix until just combined. Transfer dough to prepared pan and place a piece of plastic wrap over the top of the dough and press it evenly into the pan. Transfer pan to the fridge and let chill until firm, around 30 minutes. While the dough is chilling, preheat oven to 325 degrees.
Dough pressed into tart pan.
When dough is chilled, cut into 8 wedges using a bench scraper or a knife. Prick or dock the dough in a pretty pattern with a wood skewer or fork. Sprinkle with sparkling sugar if using. Bake until golden brown and firm in the center, around 40 to 45 minutes.