Vanilla Sandwich Cookies

In a large mixing bowl, beat 226g softened unsalted butter (for cookie dough) and 150g granulated sugar with an electric mixer on medium speed for 3 minutes, until the mixture is pale, fluffy, and light lemon-yellow. Add the room-temperature egg and 10ml vanilla extract (for dough), then beat on low speed for 30 seconds until fully combined, scraping down the bowl sides once halfway through mixing.

In a separate medium bowl, whisk together 280g all-purpose flour, 2g baking powder, and 1g fine table salt to evenly distribute leavening and salt. Add the dry mixture to the wet butter mixture in 3 equal batches, stirring on the lowest mixer speed for 20 seconds per batch, just until no dry flour streaks remain—do not overmix. Form the finished dough into a 2cm-thick flat disc and wrap tightly in plastic wrap.

Place the wrapped dough disc in the refrigerator to chill for 30 minutes, until firm enough to roll without sticking. Once chilled, unwrap dough and roll on a lightly floured surface to a uniform 5mm (1/4 inch) thickness. Use a 5cm (2 inch) round cookie cutter to cut even circles, re-rolling dough scraps once to cut additional rounds for a total of 24 equal cookie pieces. Arrange cutouts 2cm apart on parchment-lined baking sheets.

Preheat oven to 175°C (350°F) while finishing dough prep. Bake one sheet of cookies at a time on the middle oven rack for 10-12 minutes, until cookie edges are just light golden brown and centers are fully set. Let cookies rest on the hot baking sheet for 5 minutes after removing from the oven, then transfer to a wire rack to cool completely to room temperature (about 20 minutes) before adding filling.

While cookies cool, prepare the buttercream filling: beat 113g softened unsalted butter (for filling) in a medium bowl on medium speed for 2 minutes until completely smooth and lump-free. Gradually add 180g sifted powdered sugar, beating on low speed for 1 minute to combine, then increase speed to medium and add 5ml vanilla extract (for filling) and 15ml heavy cream. Beat for 1 additional minute until the filling is light, fluffy, and spreadable, adding 1ml extra cream if the mixture is too thick.

Once cookies are fully cooled, match rounds into pairs of similar size and shape. Spoon or pipe 15g (1 tablespoon) of vanilla filling onto the flat bottom side of one cookie per pair, then press the matching cookie flat-side down onto the filling with gentle even pressure until the filling spreads to 2mm from the cookie edge. Repeat for all pairs, then let assembled cookies set for 10 minutes before serving.