Use this recipe when making our Sugar Plum Tart.
Preheat oven to 375 degrees. Process nuts with 3 tablespoons sugar in a food processor until finely ground.
Put butter and remaining 1/2 cup sugar in the bowl of an electric mixer fitted with the paddle attachment; cream on medium speed until pale and fluffy, about 2 minutes. Add egg and yolk; mix 2 minutes. Add nut mixture, flour, vanilla seeds, and salt; mix on medium-high until pale and fluffy, about 3 minutes.
Refrigerate in an airtight container until ready to use, up to 3 days.