In a medium bowl, whisk together the flour & baking powder. Set aside.
Using a food processor or similar, pulse together the pecans & sugar until finely ground - about 30-seconds. Be careful not to grind for too long, as the nuts will start to release oils.
In a large bowl, combine the pecan mix, the cooled butter, and the vanilla extract. Beat together until well combined, scraping down the mixing bowl. Add the egg yolks and beat until homogenous.
With the mixer on low, slowly add the flour until just incorporated and come together. Divide the mixture in two, and wrap each half well in cling film. Shape the halves into disks and place in the fridge for 1.5-2-hours, until firm.
Preheat the oven to 180°C & line two baking trays with parchment paper. Set aside.
Remove one disk from the fridge. In between two sheets of parchment paper, roll the dough out to 1/4-inch thick. Lightly dip your cookie cutter in flour & cut out as many cookies as you can - rerolling out the scraps as needs be. The dough is extremely soft, so speed is needed. If at any point it gets too warm to work with, pop the whole tray into the freezer for 5-minute increments. Place on to one of the prepared sheets & pop back in the fridge for at least 15-minutes.
Repeat this rolling out process with the second disk of dough, ensuring that you get the same amount of cookies. Using a smaller cookie cutter, punch out holes from the centre of each cookie. Place on the second tray & return to the fridge for at least 15-minutes.
Bake the cookies in the preheated oven for 8-10 minutes, rotating the trays half way through. The cookies should be lightly golden with set edges, but they will still be very soft. Leave to cool on the baking tray for 10-minutes, before transferring to a wire rack to cool completely.
Dust the cutout cookies with a light layer of icing sugar. Turn over the whole cookies & spread with a layer of your desired fillings, before popping a cutout cookie on top and sandwiching the two together.