01 - Whisk together flour, baking powder, and salt in medium bowl. Set aside for later use.
02 - Beat butter and granulated sugar on medium speed until light and fluffy, approximately 2–3 minutes.
03 - Incorporate egg and vanilla extract, mixing until thoroughly combined.
04 - Gradually add dry ingredients to wet mixture, mixing just until flour is incorporated. Avoid overmixing.
05 - Divide dough in half, flatten into discs, wrap in plastic wrap. Refrigerate minimum 30 minutes for easier handling.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
07 - On lightly floured surface, roll one dough disc to ¼ inch thickness. Cut rounds using 2-inch cookie cutter. Place 1 inch apart on prepared sheets.
08 - Bake for 8–10 minutes until edges begin turning golden. Cool on sheets 2 minutes, then transfer to cooling racks.
09 - Beat butter until creamy. Gradually add powdered sugar, milk, vanilla, and salt. Beat until smooth and fluffy consistency achieved.
10 - Divide buttercream among small bowls. Tint each portion with different pastel food coloring, mixing until uniform color achieved.
11 - Spread or pipe generous layer of buttercream onto flat side of half the cookies. Top with remaining cookies to form sandwiches.
12 - Allow assembled cookies to set for 20 minutes before serving to prevent filling from shifting.