MAKE VANILLA WAFER COOKIES

RECIPE PREP: Line 3 baking trays with parchment paper or reusable silicone baking mats.

1. In the bowl of a stand mixer with paddle attachment, cream softened butter and sugar together. With a rubber spatula, scrape down the bottom and sides of the bowl. Mix 2 to 3 minutes on medium-high until the mixture is light and fluffy. 
2. Add vanilla extract, lemon juice and salt. Mix well. Add flour in 2 parts, mixing after each addition. Scrape down bottom and sides of the bowl. Add cornstarch. Continue mixing until the dough moves away from the sides of the bowl. The dough should be beautifully supple.
3. Transfer dough to a work surface. With a rolling pin, roll out dough until just under 1/4-inch thick. Cut out 28 wafer cookies with a round (2-inch) fluted-edge biscuit cutter. If the dough sticks to the board, lightly sprinkle the dough with powdered sugar and briefly knead it in. Or lightly dust the board with flour. Transfer cookies to a prepared baking tray. Stamp the tops with 2 to 4 lines using the biscuit cutter handle or the tines of a fork.
4. Preheat oven to 350°F. Put a tray of cookies in the freezer for 15 minutes. Remove from freezer and bake 14 minutes, or until the sides of the cookies have set. The bottoms should still be pale with a few areas that are golden blonde. Let cookies cool on the tray for 5 minutes before transferring to a cooling rack. As a tray of cookies enters the oven, slide the next tray of cookies into the freezer to chill.

MAKE VANILLA CREME FILLING

1. In a mixing bowl, cream butter and sugar together. 
2. Add vanilla extract and lemon juice. Mix to incorporate.
3. Do a taste test. If mixture is too sweet, add a tiny pinch of salt. 
4. Continue mixing until filling is smooth with no lumps. 

ASSEMBLE SANDWICH COOKIES

Once vanilla wafers are completely cooled, assemble the sandwich cookies.

1. Add 1 tablespoon filling to the center of 14 wafer cookies. 
2. With 2 fingertips, slightly flatten the filling into a disk. 
3. Top with remaining wafer cookies. 
4. With your fingertips, gently apply even pressure to the top of the cookie until the frosting has evenly spread to the edges.