Preheat oven to 350 degrees F.
Spread the nuts out in one layer on a jelly roll pan and bake them, stirring occasionally, until they are well browned, about 10 to 13 minutes (they will smell toasted and nutty). Transfer the pan to a wire rack to cool.
In a food processor, grind the nuts with 1/4 cup of the flour. Set aside.
Using an electric mixer, beat the butter and sugar until creamy and smooth, about 2 minutes. Add the vanilla and beat well. Sift together the remaining 1 3/4 cups flour, the salt, and the baking powder, and add it to the dough, mixing until just combined. Stir in the nut mixture. Form the dough into a disk, wrap in plastic wrap, and chill for at least 3 hours.
Preheat oven to 325 degrees F.
Roll the dough in between two sheets of waxed paper to 3/16-inch thick. Using a sharp knife, cut the dough into 1-inch squares, then cut the squares on a diagonal into triangles. Sprinkle the cookies with the turbinado sugar. Place them 1-inch apart on ungreased cookie sheets (do not re-roll the scraps). Prick the cookies with a fork and bake until pale gold all over, about 10 minutes. Cool on a wire rack.
Recipe courtesy of Claudia Fleming