01 - Whisk eggs, egg yolks, sugar, and Meyer lemon juice in a heatproof bowl. Set over simmering water creating 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 touching the surface, and refrigerate for at least 1 hour until set.
02 - Cream butter and sugar together until light and fluffy. Incorporate egg yolk and vanilla extract, mixing until fully combined. In a separate bowl, whisk together flour, ground almonds, cinnamon, and salt. Gradually blend dry ingredients into wet mixture until dough forms. Divide dough in half, shape into disks, wrap tightly, and refrigerate for minimum 1 hour.
03 - Preheat oven to 350°F. Roll chilled dough on lightly floured surface to 1/8-inch thickness. Cut 2-inch rounds from dough. Cut small heart or circle shapes from center of half the rounds to create windows. Transfer to parchment-lined baking sheets. Bake 10-12 minutes until edges turn golden. Cool completely on baking sheet.
04 - Generously dust windowed cookie tops with powdered sugar. Spread small amount of chilled Meyer lemon curd onto solid cookie bases. Gently press windowed tops onto curd-covered bases. Repeat with remaining cookies. Refrigerate assembled cookies briefly to set filling before serving.