01 - Whisk together eggs, egg yolks, sugar, and Meyer lemon juice in a heatproof bowl. Set over a pot of simmering water to create a double boiler. Whisk constantly until mixture thickens and coats the back of a spoon, approximately 8-10 minutes, reaching 170-175°F. Remove from heat and whisk in butter and lemon zest until smooth. Transfer to a bowl, cover with plastic wrap directly touching the surface, and refrigerate for at least 1 hour until set.
02 - Cream butter and sugar in a bowl until light and fluffy. Beat in egg yolk and vanilla extract until fully incorporated. In a separate bowl, whisk together flour, ground almonds, cinnamon, and salt. Gradually mix dry ingredients into wet mixture until dough forms. Divide dough into two portions, shape each into a disk, wrap separately, and refrigerate for at least 1 hour.
03 - Preheat oven to 350°F. Roll dough on lightly floured surface to 1/8-inch thickness. Cut 2-inch rounds from dough. Use a small cutter to create windows in the center of half the rounds. Transfer to parchment-lined baking sheets. Bake for 10-12 minutes until edges are golden brown. Cool completely on wire racks.
04 - Dust windowed cookie tops generously with powdered sugar. Spread a small amount of chilled Meyer lemon curd onto each solid bottom cookie. Gently press a windowed cookie onto each curd-topped base. Refrigerate assembled cookies briefly to set filling before serving.