Put the pecans and flour in the bowl of a food processor, and pulse until the pecans are finely ground, scraping down the sides and bottom of the bowl as needed so the nuts are as evenly grounded as possible. Transfer to a large mixing bowl, and whisk in the kosher salt and baking powder. Reserve.

In the bowl of a stand mixer fitter with the paddle attachment (or in a large mixing bowl, if you’re using a handheld mixer), beat the unsalted butter or dairy-free shortening, sugar, and vanilla together until the mixture is fluffy and pale, about 3 minutes. Add the egg yolk and beat well. Add the flour and pecan mixture and mix at low speed until the dough is just combined, about 1 minute. The dough will look crumbly, and that’s OK. Dump about half of the dough mixture onto a square of plastic wrap. Using your hands, bring the dough together into a flat ball, wrap tightly, and refrigerate 30 minutes. Repeat for the second half of the dough. While dough is resting, make ganache.

Preheat oven to 325°F. Line a baking sheet with parchment paper.

Place the first ball of dough over a large square of parchment paper set directly on a flat countertop (see note at the end of the recipe). Place a second square of parchment paper over the dough and then roll the dough out (rolling the pin over the parchment paper) until ¼ inch thick. Using a 3-inch round cookie cutter, or cookie cutter of your choice, cut out as many shapes as possible, carefully transferring each cookie onto one of the prepared baking sheets (a pastry spatula helps to lift and transfer the cookies.) Make sure to set the cookies about 2 inches apart because they will spread a little while baking. Gather the scraps, reroll, and cut out new shapes, repeating until there is no dough left.

When you fill up a baking sheet, transfer to the oven and bake the cookies for 15 to 20 minutes until pale golden on the edges. Store the remaining dough in the fridge in between batches. (You can prepare a second sheet of cookies while the first one bakes to save time.) Cool the cookies for a few minutes on the baking sheet, and then transfer to a wire rack to cool completely. You can make the cookies ahead of time; simply store them in an airtight container at room temperature or in the refrigerator until you’re ready to assemble them.

Spread a thick layer of ganache on the underside of a cookie, and then cover with another cookie. Repeat to assemble all cookies.

Take the cookies out of the refrigerator 20 minutes before serving to return them to room temperature before enjoying.