01 - In a medium bowl, whisk together the flour, baking powder, and salt until evenly combined. Set aside for later use.
02 - In a large mixing bowl, beat the butter and granulated sugar on medium speed until light and fluffy, approximately 2–3 minutes.
03 - Add the egg and vanilla extract to the butter mixture, mixing until fully incorporated and smooth.
04 - Gradually add the dry ingredients to the wet mixture, mixing just until the flour disappears and a soft dough forms. Avoid overmixing.
05 - Divide the dough in half and flatten each portion into discs. Wrap tightly in plastic wrap and refrigerate for at least 30 minutes until firm.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper and set aside.
07 - On a lightly floured surface, roll one dough disc to ¼ inch thickness. Cut rounds using a 2-inch cookie cutter. Place cookies 1 inch apart on prepared baking sheets.
08 - Bake for 8–10 minutes or until edges just begin to turn golden. Let cool on sheets for 2 minutes, then transfer to wire racks to cool completely.
09 - Beat the butter until creamy. Gradually add powdered sugar, milk, vanilla, and salt, beating until smooth and fluffy.
10 - Divide the buttercream into small bowls. Tint each portion with a different pastel gel food coloring, mixing until uniform color is achieved.
11 - Spread or pipe a generous layer of buttercream onto the flat side of half the cookies. Top with remaining cookies to create sandwiches.
12 - Allow assembled cookies to set for 20 minutes at room temperature before serving to ensure filling holds its shape.