Preheat the oven to 355°F. Line two 8x11-inch baking sheets with parchment paper.
In a large bowl, whisk together brown rice flour, almond flour, corn flour, potato starch, and salt. Set aside.
In the bowl of a stand mixer, preferably fitted with a paddle attachment, cream butter, sugar, and vanilla seeds together, until a thick paste forms – about 20-40 seconds.
Add the dry ingredients to the butter mixture, and mix until a dough forms, about 2 minutes. Add egg yolks and 1 tablespoon of water and continue mixing until the dough comes together in a ball. Add more water if the dough is too dry, sandy, and doesn’t come together. The dough should be smooth and a bit wet, but you should be able to handle it with your hands without sticking.
Turn the dough out onto the lightly floured counter and shape into a disk. Using a rolling pin, roll the dough out, about ⅓-inch thick. Cut using a star-shaped cutter and place cookies on the prepared baking trays.
Bake until lightly golden brown on the edges and aromatic, about 12 minutes. Transfer to a wire rack. Let cool completely, then dust with powdered sugar and store in an airtight container at room temperature for up to 3 days.
Tip: These cookies freeze beautifully! Just place them in an airtight container or freezer bag and keep frozen for up to three months.
*You can replace these flours with equal parts gluten-free all-purpose flour blend of your choice.