Preheat the oven to 350 degrees F. Spread the pecans on a rimmed baking sheet and bake until browned, 10 to 12 minutes. Let cool completely. Sift 3/4 cup flour, the salt and baking powder into a medium bowl.
Pulse the toasted nuts with the remaining 2 tablespoons flour in a food processor until finely ground.
Beat the butter, confectioners' sugar and vanilla in a large bowl with a mixer on medium-high speed until light and fluffy, 3 to 5 minutes. Add the flour mixture and stir with a wooden spoon until just combined, then stir in the nut mixture. Pat the dough into a rectangle on a piece of plastic wrap; wrap and refrigerate until firm, at least 2 hours or overnight.
Position racks in the upper and lower thirds of the oven and preheat to 325 degrees F. Line 2 baking sheets with parchment paper. Roll out the dough between 2 pieces of parchment into a 9-by-6-inch rectangle, slightly less than 1/4 inch thick. Sprinkle the dough with turbinado sugar, then gently press the sugar into the dough using a rolling pin. Slice into sixths crosswise and lengthwise to make 36 rectangles. Arrange about 1 inch apart on the prepared baking sheets. Pierce each rectangle a few times with a fork, then press a pecan onto each. Bake, switching the position of the pans halfway through, until golden brown, 10 to 12 minutes. Let cool 3 minutes on the baking sheets, then transfer to racks to cool completely.