Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.
In a mixing bowl, whisk together the all-purpose flour, baking powder, and salt until well combined. Set aside.
In another large mixing bowl, beat the softened butter and granulated sugar together using an electric mixer until light and fluffy.
Add the egg and vanilla extract to the butter mixture and beat until fully incorporated.
Gradually add the flour mixture to the wet ingredients, mixing until just combined. Do not over-mix.
Divide the dough into two portions and wrap each in plastic wrap. Chill in the refrigerator for at least 1 hour.
On a floured surface, roll out the dough to about ¼ inch thickness. Use Easter-themed cookie cutters to cut out shapes and place them on prepared baking sheets.
Bake the cookies in the preheated oven for 10 to 12 minutes, or until the edges are lightly golden. Allow them to cool on a wire rack.
To make the royal icing, combine powdered sugar, egg whites (or meringue powder mixture), and lemon juice in a mixing bowl. Beat until the icing holds stiff peaks.
If desired, divide the royal icing into small bowls and add food coloring to create different colors.
Transfer the icing into piping bags or squeeze bottles. Decorate the cooled cookies as desired.
Allow the royal icing to dry completely before storing the cookies in an airtight container.