01 - In a medium saucepan, whisk together Meyer lemon juice, zest, sugar, egg yolks, and salt. Add butter cubes. Cook over medium-low heat, whisking constantly, until the mixture thickens and coats the back of a spoon, approximately 8 to 10 minutes. Do not allow the mixture to boil.
02 - Pour the curd through a fine-mesh sieve into a clean bowl to remove any cooked egg bits. Press plastic wrap directly onto the surface to prevent a skin from forming. Refrigerate for at least 1 hour until completely set.
03 - In a medium bowl, whisk together all-purpose flour, almond flour, baking powder, and salt until evenly blended.
04 - In a large bowl, beat softened butter and powdered sugar using a stand mixer or electric hand mixer until light and fluffy, about 2 to 3 minutes. Beat in the egg yolk, vanilla extract, and Meyer lemon zest until fully incorporated.
05 - Gradually add the dry ingredients to the butter mixture, mixing just until combined. Divide the dough in half and flatten each portion into a disc. Wrap tightly in plastic wrap and refrigerate for at least 1 hour.
06 - Preheat the oven to 350°F. Line two baking sheets with parchment paper and set aside.
07 - On a lightly floured surface, roll out one disc of dough to 1/8 inch thickness. Cut out rounds using a 2-inch cookie cutter. For half of the cookies, use a smaller cutter to create a window shape in the center. Re-roll scraps as needed.
08 - Arrange cookies 1 inch apart on the prepared baking sheets. Bake for 10 to 12 minutes, until edges are just beginning to turn golden. Let cool on the baking sheet for 2 minutes, then transfer to a wire rack to cool completely.
09 - Dust the window-cut cookies generously with powdered sugar. Spread approximately 1 teaspoon of chilled Meyer lemon curd onto the flat side of each solid cookie. Gently press a window cookie on top to create sandwiches.