Whisk the flour, cocoa powder, baking powder, and salt together in a medium bowl. Set aside.

In a large bowl using a handheld or a stand mixer fitted with a paddle attachment, beat the butter and sugar together on high speed until completely smooth and creamy, about 2 minutes. Add the egg and vanilla and beat on high speed until combined, about 1 minute. Scrape down the sides and up the bottom of the bowl and beat again as needed to combine.

Add the dry ingredients to the wet ingredients and mix on low until combined. Dough will be soft. If the dough seems too soft and sticky for rolling, add 1 more Tablespoon of flour.

Divide the dough into 2 equal parts. Dust 2 large pieces of parchment paper or 2 silicone baking mats with cocoa powder or flour. Place a dough half on each. With a rolling pin lightly dusted with cocoa powder or flour, roll the dough out to about 1/4-inch thickness. Use more cocoa powder/flour if the dough seems too sticky. The rolled-out dough can be any shape, as long as it is evenly 1/4-inch thick.

Lightly dust one of the rolled-out doughs with cocoa powder or flour. Place a piece of parchment on top. (This prevents sticking.) Place the 2nd rolled-out dough on top. Cover with plastic wrap or aluminum foil, then refrigerate for at least 1-2 hours and up to 2 days.

Once chilled, preheat oven to 350°F (177°C). Line 2-3 large baking sheets with parchment paper or silicone baking mats. Carefully remove the top dough piece from the refrigerator. Using cookie cutters, cut the dough into shapes. Re-roll the remaining dough, using more cocoa powder or flour to lightly dust your work surface and rolling pin, and continue cutting the dough until all is used. Work quickly so the dough doesn’t become too warm or soft. If it does, stop what you’re doing and place any unused dough back in the refrigerator for 10 minutes to stiffen up again. Repeat cutting into shapes with 2nd half of dough. (Note: It doesn’t seem like a lot of dough, but you get a lot of cookies from the dough scraps you re-roll.)

Arrange shaped cookies on baking sheets 3 inches apart. Bake for 11-12 minutes or until edges are set. If your oven has hot spots, rotate the baking sheet halfway through bake time. Allow cookies to cool on the baking sheet for 5 minutes and then transfer to a wire rack to cool completely before decorating.

Prepare the royal icing, cookie glaze icing, or cookie decorating buttercream, and decorate the cooled cookies however you’d like. I decorated the pictured chocolate sugar cookie hearts with cookie decorating buttercream, piped on with a Wilton 1A piping tip. Then I spread it around to flatten it out, and topped with these sprinkles. This is a classic vanilla buttercream frosting that soft-sets on cookies after a few hours.

Enjoy cookies right away or wait until the frosting/icing sets to serve them. Once the icing has set, these cookies are great for gifting or for sending. Plain or decorated cookies stay soft for about 5 days when covered tightly at room temperature. For longer storage, cover and refrigerate for up to 10 days.