In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt until well combined. Set aside.

In a large bowl, beat the softened butter and granulated sugar on high speed until smooth and creamy, about 2 minutes.

Add the egg and vanilla extract to the butter and sugar mixture and beat on high speed until fully combined, about 1 minute. Scrape down the sides and bottom of the bowl to blend well.

Gradually add the dry ingredients into the wet mixture, mixing on low speed until fully combined. If the dough feels too sticky, add 1 more tablespoon of flour.

Divide the dough into two equal parts. Dust parchment paper or silicone mats lightly with cocoa powder or flour. Roll each dough half to about 1/4-inch thickness.

Lightly dust one rolled-out dough with cocoa powder. Stack the two rolled-out doughs, cover with plastic wrap, and refrigerate for at least 1-2 hours or up to 2 days.

Preheat your oven to 350°F (177°C). Line 2-3 baking sheets with parchment paper or silicone mats.

Once the dough is chilled, use cookie cutters to cut out shapes. Reroll any remaining dough and cut out more shapes.

Place cookie shapes on the baking sheets, leaving 3 inches of space between each. Bake for 11-12 minutes or until the edges are set.

Cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

Once cooled, prepare royal icing and decorate the cookies as desired. Add sprinkles for a festive touch.

Allow decorated cookies to set before serving or storing.