In a large mixing bowl, cream butter and sugar together using a hand mixer on medium speed until light and fluffy, about 2 minutes.

Add egg and vanilla and beat until combined.

Turn the mixer to low speed and add baking powder and salt.

Gradually add flour and mix until combined.

Form the dough into a ball and wrap it tightly in plastic cling wrap. Freeze for 30 minutes or refrigerate until firm (at least 1 hour, up to overnight).

Preheat the oven to 350 F.

Line a half sheet baking pan with parchment paper or silicone baking mat.

Remove the dough from refrigerator and let it sit at room temperature for 5-10 minutes. On a lightly floured surface, use a rolling pin to roll the dough out until it is ¼-inch thick. Use an egg-shaped cookie cutter to cut out Easter egg cookie shapes. Transfer the cookies onto the lined baking sheet, placing them one inch apart. Re-roll any scraps and repeat to cut out more cookies.

Bake cookies for 8-10 minutes, until the edges start to turn golden brown.

Let the cookies cool for a couple minutes on the baking sheet, then transfer them to a wire cooling rack to cool completely.

In a medium mixing bowl, combine confectioners' sugar with meringue powder. Add water and vanilla extract and beat with a hand mixer on medium-high speed, until smooth. Adjust icing consistency as needed.

Use a no. 5 piping tip to outline the base color on the sugar cookie, leaving about ⅛-inch from the edge, and fill in the inside. Use the back of a spoon to spread the icing to the edge. Allow to dry about 20-30 minutes before decorating with a thin no. 1 round tip to add patterns.

Allow the icing to set completely before storing.