01 - Whisk together Meyer lemon juice, zest, sugar, egg yolks, and salt in a medium saucepan. Add butter cubes. Cook over medium-low heat, whisking constantly, until the mixture thickens and coats the back of a spoon, about 8-10 minutes. Do not let the mixture boil.
02 - Strain the curd through a fine-mesh sieve into a clean bowl. Press plastic wrap directly onto the surface to prevent a skin from forming. Refrigerate until set, at least 1 hour.
03 - In a medium bowl, whisk together all-purpose flour, almond flour, baking powder, and salt until evenly combined.
04 - Beat softened butter and powdered sugar in a large bowl until light and fluffy, about 2-3 minutes. Incorporate egg yolk, vanilla extract, and Meyer lemon zest until smooth.
05 - Gradually add dry ingredients, mixing just until combined. Divide dough in half, flatten into discs, and wrap tightly in plastic. Refrigerate for at least 1 hour until firm.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
07 - Roll out one dough disc on a lightly floured surface to 1/8 inch thickness. Cut out 2-inch rounds. For half the cookies, cut a small heart or round from the center to create windows. Re-roll scraps as needed.
08 - Arrange cookies 1 inch apart on prepared baking sheets. Bake for 10-12 minutes until edges are just golden. Let cool on sheets for 2 minutes, then transfer to wire racks to cool completely.
09 - Generously dust window-cut cookies with powdered sugar. Spread 1 teaspoon of chilled Meyer lemon curd on the flat side of each solid cookie. Gently press a window cookie on top to complete the sandwich.