01 - Whisk together eggs, egg yolks, sugar, and Meyer lemon juice in a heatproof bowl. Set over a simmering pot of water creating a double boiler. Whisk constantly until mixture thickens and coats the back of a spoon, about 8-10 minutes until reaching 170-175°F. Remove from heat immediately. Whisk in butter cubes and lemon zest until completely smooth and emulsified. Transfer curd to a clean bowl and press plastic wrap directly onto the surface to prevent skin formation. Refrigerate for at least 1 hour until completely set and chilled.
02 - Cream butter and granulated sugar in a mixing bowl until light and fluffy, approximately 3 minutes. Add egg yolk and vanilla extract, mixing until fully incorporated. In a separate bowl, whisk together flour, ground almonds, cinnamon, and salt. Gradually add dry ingredients to wet mixture, mixing just until dough forms and no dry streaks remain. Divide dough into two equal portions. Shape each into a flat disk, wrap tightly in plastic wrap, and refrigerate for at least 1 hour until firm and easy to handle.
03 - Preheat oven to 350°F and line baking sheets with parchment paper. On a lightly floured surface, roll chilled dough to 1/8-inch thickness. Using a 2-inch round cutter, cut out cookies. For half of the rounds, use a small heart or round cutter to create a window in the center. Transfer cookies to prepared baking sheets, spacing 1 inch apart. Bake for 10-12 minutes until edges are lightly golden. Cool on baking sheets for 5 minutes, then transfer to wire racks to cool completely.
04 - Generously dust the windowed cookies with powdered sugar using a fine-mesh sieve. Spread approximately 1 teaspoon of chilled Meyer lemon curd onto each solid bottom cookie, leaving a small border around the edge. Gently place a windowed cookie on top, pressing lightly to create a sandwich without squeezing out the filling. Repeat with remaining cookies. Refrigerate assembled cookies for 15-20 minutes to allow the curd to set slightly before serving.