Eggy Lemon Sandwich Cookies

To make the cookies, in a medium bowl whisk together flour, baking soda, and salt.

In the bowl of a stand mixer fitted with a paddle attachment, cream together shortening and butter until well combined. Scrape down the sides of the bowl, add the sugar and beat on medium speed until pale and fluffy, 3 to 5 minutes.

Add the egg, milk, and vanilla extract and beat until combined. Stop the mixer. Add the dry ingredients and beat on low until a dough forms. Scrape down the sides of the bowl to ensure no dry pockets are hidden at the bottom of the bowl. Wrap and refrigerate dough for 30 minutes.

Place a rack in the upper third of the oven and preheat oven to 350 degrees F. Roll half of the dough between two lightly floured pieces of parchment paper or on a lightly floured counter to a thick ¼-inch thickness of just under 1/2-inch thickness. Cut with a 2 to 3-inch egg cookie cutter and place on a parchment lined baking sheet. Use a 1-inch round or egg-shaped cookie cutter to cut yolk holes out of half of the egg cookies. This will be our top cookie. Bake for 8 to 10 minutes until just golden around the edges. Allow to cool completely before filling.

To make the lemon curd, whisk together juice, zest, sugar, and eggs in a 2-quart heavy saucepan. Stir in butter and cook over moderately low heat, whisking frequently, until curd is thick enough to hold marks of whisk and first bubble appears on surface, about 6 minutes. Transfer lemon curd to a bowl and chill, its surface covered with plastic wrap, until cold, at least 1 hour. The curd will thicken as it cools.

To make the buttercream, in a medium bowl with an electric hand mixer, beat butter until well softened around the bowl.  Add powdered sugar, salt, and lemon zest and beat on low speed.  Add the warm milk and whip to combine. Beat in poppy seeds. Transfer frosting to a freezer ziplock bag with the corner tip cut off or a piping bag with a medium round tip. Leave buttercream at room temperature until ready to pipe.

To assemble the cookies, flip each whole egg cookie so the bottom is facing up.  Pipe buttercream frosting around the edge.  Spoon 2-3 teaspoons of lemon curd into the center of the cookie. Top with a cookie with a hole, press gently to sandwich and spoon a teaspoon of lemon curd into the cookie hole.  Store in the refrigerator and dust with powdered sugar before serving. Cookies will last up to 3 days in the refrigerator.