Cream together the softened butter and granulated sugar until light and fluffy, about 3-5 minutes. Beat in the egg and vanilla extract. Gradually add the flour and a pinch of salt until a soft dough forms. Chill the dough in the refrigerator for at least 30 minutes.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper. Roll out the chilled dough to about 1/4 inch thick. Use butterfly-shaped cookie cutters to cut out shapes, placing them on prepared baking sheets with 2 inches of space between each cookie. Bake for 8-10 minutes until edges are lightly golden.

While the cookies cool, prepare the royal icing by mixing powdered sugar, meringue powder, and water. Whisk until smooth and glossy. Divide the icing into bowls and color each with gel food colors.

Using a piping bag, outline the top part of each butterfly with black icing. Flood the center sections with pink icing, ensuring there's sufficient icing to hold its shape.

While the icing is still wet, use a needle tool to create designs by gently dragging through the different colors. Work quickly to avoid drying.

Outline and flood the bottom wings with preferred colors and add small white dots for detail. Allow the icing to set for about 30 minutes.

Pipe a thin line down the center of each butterfly cookie to form the body and add black sanding sugar for texture. Allow the cookies to dry on a wire rack for 4-6 hours or overnight for best results.