Mix the flour, baking powder, and salt together in a medium bowl. Set this dry mixture aside.
Use an electric mixer to cream the softened butter and sugar in a large bowl until the mixture is light and fluffy.
Add the egg and vanilla to the creamed mixture and mix until just combined.
Gradually mix the dry ingredients into the wet ingredients until a dough forms. Do not overmix.
Wrap the dough in plastic wrap and chill it in the refrigerator for 1 hour.
Preheat your oven to 175°C (350°F). Line baking sheets with parchment paper.
On a lightly floured surface, roll the chilled dough out to about 1/4 inch thickness. Cut out your desired shapes.
Place the cutouts onto the prepared baking sheets. Bake for 8 to 10 minutes, or until the edges are lightly golden.
Remove the cookies from the oven and let them cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.
Prepare the icing: Whisk together the powdered sugar and meringue powder. Slowly add the water, one tablespoon at a time, until you reach a smooth, thick consistency suitable for outlining.
Divide the icing into separate small bowls and tint each portion with a different pastel gel color.
Outline the cooled cookies with the desired color. Once the outline sets, flood the center with the same or a different color. Let the icing dry completely.
Add decorative details like dots, lines, or Easter patterns using the remaining icing once the base layer is dry.