Stir in vanilla, lemon juice, and salt, stirring until well combined, and scrape down the sides of the bowl using a rubber spatula to ensure ingredients are well incorporated.
Add egg yolk and beat until combined.
1 large egg yolk
Gradually add flour and salt, use a silicone spatula until well incorporated (you will need to scrape down the sides and the bottom of the bowl several times for this, as the mixture is fairly dry and crumbs tend to settle at the bottom of the bowl).
2 ¼ cups all-purpose flour, ½ teaspoon salt
Transfer the dough to a clean surface and use your hands to form it into a cohesive ball.
Flatten into a disk (about 1″ thick), cover with clear wrap, and chill for 15 minutes.
Preheat oven to 350°F.
Once the dough has chilled, transfer it to a clean, lightly floured surface and use a lightly floured rolling pin to roll it out to about ¼” thickness.
Lightly flour your cookie cutters and cut out your shapes, transferring them to a greased cookie sheet, and placing them at least 1″ apart.
Once you have cut out all of the shapes that you can, be sure to re-combine the scraps and roll out and cut out again to get the maximum number of cookies from your dough.
Bake at 350F for 9-10 minutes and allow cookies to cool completely before filling them with lemon cream.
Lemon Filling:
In a large bowl, beat the softened butter until creamy, about 2 minutes.
½ cup unsalted butter
Gradually add the sifted powdered sugar, beating on low speed until combined.
1 ¾ cups powdered sugar
Add vanilla extract and lemon zest and beat until smooth.
1 tsp vanilla extract, 1 tsp lemon zest
Add heavy cream or milk, 1 tablespoon at a time, until the filling reaches a smooth and spreadable consistency.
1-2 tablespoons heavy cream or milk
Assembling the Cookies:
Pair the cooled cookies.
Using a piping bag, spread a generous amount of the crème filling on the flat side of one cookie.
Place another cookie on top and gently press together to create a sandwich.
Notes
Chill the Dough: If your dough seems sticky, cover dough in plastic wrap and chill it for about 15 minutes. It’s much easier to roll out that way.
Use a Paddle Attachment: If you have a stand mixer, try using the paddle attachment for an even mix. If not, a hand mixer or good ol’ elbow grease works fine.
Roll Evenly: For a uniform thickness, place two rulers or a dough guide on each side of your dough. This helps the cookies bake evenly—no thin edges or thick centers.
Watch the Oven: These cookies can go from soft to over-browned quickly, so keep a close eye. The edges should be lightly golden for the best way to maintain a soft texture.
Taste Test the Filling: If you want more “zing,” add a few more drops of lemon extract or a bit of extra fresh lemon. If it’s too tangy, throw in a bit more powdered sugar for balance.
Divide Dough: Rolling out a smaller portion of dough at a time is easier. Keep the rest in the fridge so it stays cool and workable.