In the work bowl of a food processor, combine flour, macadamia nuts, brown sugar, and salt; process until mixture is combined. Add butter, and process until mixture is crumbly. Add egg yolk and 2 tablespoons water; process until mixture comes together.
Press dough into a disk, wrap in plastic wrap, and refrigerate for at least 1 hour or up to 3 days.
Preheat oven to 400°.
On a lightly floured surface, roll dough to a ⅛-inch thickness. Using a 6-inch round cutter, cut dough. Press into bottom and up sides of 12 (4-inch) round tart pans with removable bottoms. Line pans with parchment paper and fill with pie weights.
Place on a baking sheet, and bake until golden brown, about 15 minutes. Remove parchment and pie weights, and let cool completely before using.
Recipe by Victoria at https://victoriamag.com/miniature-coconut-cream-macadamia-nut-tarts-recipe/