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 to 10 minutes. Do not let the mixture boil.
02 - Strain the curd through a fine-mesh sieve into a bowl. Cover with plastic wrap directly on 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 well combined.
04 - In a large bowl, beat butter and powdered sugar until light and fluffy, about 2 to 3 minutes. Beat in egg yolk, vanilla extract, and Meyer lemon zest until smooth.
05 - Gradually add the dry ingredients to the butter mixture, mixing just until combined. Divide dough in half, flatten into discs, and wrap in plastic. Refrigerate 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 in diameter. For half the cookies, cut a small shape from the center to form windows.
08 - Arrange cookies 1 inch apart on prepared baking sheets. Bake 10 to 12 minutes, until edges are just golden. Cool on the sheet for 2 minutes, then transfer to a wire rack to cool completely.
09 - Dust the window cookies generously 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 form a sandwich.