01 - Whisk together Meyer lemon juice, zest, granulated sugar, egg yolks, and salt in a medium saucepan. Add cubed butter. Cook over medium-low heat, whisking continuously until the mixture thickens enough to coat 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 and chilled.
03 - In a medium bowl, combine all-purpose flour, almond flour, baking powder, and salt. Whisk thoroughly to ensure the almond flour is evenly distributed throughout the mixture.
04 - Beat softened unsalted butter and powdered sugar in a large bowl until the mixture becomes pale and fluffy, about 2 to 3 minutes. Add the egg yolk, vanilla extract, and Meyer lemon zest. Beat until fully incorporated and smooth.
05 - Gradually add the dry ingredients to the butter mixture, mixing only until just combined. Avoid overworking the dough. Divide into two equal portions, flatten each into a disc, wrap tightly in plastic wrap, and refrigerate for a minimum of 1 hour.
06 - Set oven temperature to 350°F. Line two baking sheets with parchment paper to prevent sticking and ensure easy cleanup.
07 - Roll one chilled dough disc on a lightly floured surface to 1/8 inch thickness. Cut into 2-inch rounds using a cookie cutter. For half of the rounds, use a small cutter to create a window shape in the center. Re-roll scraps as necessary to maximize yield.
08 - Arrange cut cookies on prepared baking sheets, leaving 1 inch of space between each. Bake for 10 to 12 minutes until edges are lightly golden. Allow cookies to rest on the baking sheet for 2 minutes before transferring to a wire rack to cool completely.
09 - Generously dust the windowed cookies with powdered sugar. Spread approximately 1 teaspoon of chilled Meyer lemon curd onto the flat side of each solid cookie. Gently press a windowed cookie onto the curd to create sandwiches. Handle delicately to prevent breakage.