01 - In a heatproof bowl, whisk together eggs, egg yolks, sugar, and Meyer lemon juice. Set over a simmering pot of water to create a double boiler, whisking constantly until mixture thickens and coats the back of a spoon, approximately 8-10 minutes or until it reaches 170-175°F. Remove from heat, whisk in butter and lemon zest until smooth. Transfer to a bowl, cover with plastic wrap placed directly on the surface, and refrigerate for at least 1 hour until set.
02 - Cream butter and sugar together until light and fluffy. Add egg yolk and vanilla, mixing until fully incorporated. In a separate bowl, whisk together flour, ground almonds, cinnamon, and salt. Gradually mix dry ingredients into wet ingredients until a cohesive dough forms. Divide dough in half, shape into two disks, wrap tightly, and refrigerate for at least 1 hour.
03 - Preheat oven to 350°F. On a lightly floured work surface, roll out dough to 1/8-inch thickness. Cut out 2-inch diameter rounds. For half of the cookies, cut a small heart or circle from the center to create windows. Transfer to parchment-lined baking sheets. Bake for 10-12 minutes until edges are golden brown. Allow cookies to cool completely on the baking sheet.
04 - Generously dust the windowed cookies with powdered sugar. Spread approximately 1 teaspoon of chilled Meyer lemon curd onto each solid bottom cookie. Carefully top with a windowed cookie, pressing gently to form a sandwich. Repeat with remaining cookies. Refrigerate briefly to set the filling before serving.