01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together flour, baking powder, and salt until well combined.
03 - In a large bowl, beat softened butter and granulated sugar with an electric mixer until light and fluffy, about 2 to 3 minutes.
04 - Beat in the egg and vanilla extract until fully incorporated into the mixture.
05 - Gradually add the dry ingredients to the wet ingredients, mixing on low speed until a smooth dough forms.
06 - Divide dough in half, flatten into disks, wrap in plastic wrap, and refrigerate for 30 minutes.
07 - On a lightly floured surface, roll out dough to 1/4-inch thickness. Cut out cookies using round or flower-shaped cutters.
08 - Place cookies 2 inches apart on prepared baking sheets. Bake for 10 to 12 minutes, or until edges are just beginning to turn golden.
09 - Let cookies cool on baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
10 - Beat softened butter in a large bowl until smooth and creamy. Gradually add sifted confectioners sugar, mixing well after each addition.
11 - Add milk, vanilla, and salt. Beat on medium-high speed for 2 to 3 minutes until fluffy. Add additional milk 1 tsp at a time if needed to achieve piping consistency.
12 - Divide buttercream into separate bowls and tint each portion with gel food coloring as desired.
13 - Fit piping bags with small star, petal, and leaf tips. Fill each bag with a different colored buttercream.
14 - Pipe flowers and leaves onto completely cooled cookies using prepared piping bags and tips.
15 - Allow decorated cookies to sit at room temperature until buttercream firms up slightly before serving or storing.