Preheat the oven to 350°F (175°C).
In a bowl, cream together butter and sugar until smooth.
Add the egg and vanilla extract and mix thoroughly.
In a separate bowl, whisk together the flour, baking powder, and salt.
Gradually combine the dry ingredients with the wet mixture.
Roll the dough out on a floured surface to desired thickness and cut into shapes.
Arrange cookies on a baking sheet and bake for 10 to 12 minutes until lightly golden.
Allow cookies to cool completely before decorating.
Prepare royal icing, divide into bowls, and tint with food coloring.
Decorate the cooled cookies with icing and sprinkles as desired.