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 (about 8–10 minutes; do not boil).
02 - Strain the curd through a fine-mesh sieve into a bowl. Cover with plastic wrap directly on the surface and chill until set, at least 1 hour.
03 - In a medium bowl, whisk together all-purpose flour, almond flour, baking powder, and salt.
04 - In a large bowl, beat butter and powdered sugar until light and fluffy (about 2–3 minutes). Beat in egg yolk, vanilla, and Meyer lemon zest.
05 - Gradually add the dry ingredients, mixing just until combined. Divide dough in half, flatten into discs, and wrap in plastic. Chill for at least 1 hour.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
07 - Roll out one disc of dough on a lightly floured surface to 1/8 inch thickness. Cut out rounds (about 2 inches). For half the cookies, cut a small shape (e.g., heart or round) from the center to form windows.
08 - Arrange cookies 1 inch apart on prepared baking sheets. Repeat with the second disc, re-rolling scraps as needed.
09 - Bake 10–12 minutes, until edges are just golden. Cool on the sheet 2 minutes, then transfer to a rack to cool completely.
10 - Dust the window cookies with powdered sugar. Spread 1 teaspoon Meyer lemon curd on the flat side of each solid cookie. Top each with a window cookie, pressing gently to sandwich.