In a medium bowl, whisk together the flour, baking powder, and salt.
3 cups all-purpose flour, 1 teaspoon baking powder, ½ teaspoon salt
In a large bowl, beat the butter and sugar until light and fluffy. Mix in the egg and vanilla extract.
1 cup unsalted butter, 1 cup sugar, 1 large egg, 1 teaspoon vanilla extract
Gradually add the dry ingredients to the wet mixture until a dough forms.
Divide the dough in half, wrap in plastic wrap, and chill in the refrigerator for at least 1 hour.
Preheat oven to 350°F (180°C). Line baking sheets with parchment paper.
On a lightly floured surface, roll out the dough to about ¼ inch thick. Cut out skull shapes with a cookie cutter and place on the prepared sheets.
Bake for 8–10 minutes, or until the edges are lightly golden. Allow cookies to cool completely before decorating.
In a bowl, whisk confectioner’s sugar with 2 tablespoons of milk or water. Add more liquid gradually until icing is smooth and slightly thick. Divide icing into small bowls and tint each with different gel food coloring.
2 cups confectioner’s sugar, 2–4 tablespoons milk or water, Gel food coloring
Create a base layer by coating the top of the cookie with the icing using a small spoon. Pipe or spread colorful designs onto each cookie to resemble traditional sugar skulls. Allow icing to set before serving.