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 thickened and coats the back of a spoon, about 8–10 minutes. Do not let boil.
02 - Strain curd through a fine-mesh sieve into a bowl. Press plastic wrap directly onto surface and refrigerate until set, at least 1 hour.
03 - Whisk together all-purpose flour, almond flour, baking powder, and salt in a medium bowl until well combined.
04 - Beat butter and powdered sugar in a large bowl until light and fluffy, about 2–3 minutes. Beat in egg yolk, vanilla, and Meyer lemon zest until incorporated.
05 - Gradually add dry ingredients, mixing just until combined. Divide dough in half, form into discs, wrap in plastic, and refrigerate for at least 1 hour.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
07 - Roll one dough disc to 1/8 inch thickness on lightly floured surface. Cut 2-inch rounds. Cut small windows from center of half the rounds. Re-roll scraps as needed.
08 - Arrange cookies 1 inch apart on prepared baking sheets. Bake 10–12 minutes until edges are just golden. Cool on sheets 2 minutes, then transfer to rack to cool completely.
09 - Dust window-cut cookies with powdered sugar. Spread 1 teaspoon lemon curd on flat side of each solid cookie. Top with window cookies, pressing gently to adhere.