01 - Whisk together eggs, egg yolks, sugar, and Meyer lemon juice in a heatproof bowl. Place over simmering water, stirring constantly until thickened and coating the back of a spoon, reaching 170-175°F. Remove from heat, incorporate butter and zest until smooth. Cover with plastic wrap directly on surface and refrigerate at least 1 hour until set.
02 - Cream butter and sugar until light and fluffy. Blend in egg yolk and vanilla until incorporated. In separate bowl, combine flour, ground almonds, cinnamon, and salt. Gradually incorporate dry mixture into wet until dough forms. Divide into two disks, wrap, and refrigerate minimum 1 hour.
03 - Preheat oven to 350°F. Roll chilled dough to 1/8-inch thickness on lightly floured surface. Cut 2-inch rounds, cutting center shapes from half to create windows. Arrange on parchment-lined baking sheets. Bake 10-12 minutes until edges are golden. Cool completely before assembling.
04 - Dust windowed tops generously with powdered sugar. Spread chilled Meyer lemon curd onto solid bottom cookies. Place windowed cookies over curd, pressing gently to secure. Refrigerate briefly to set filling before serving.