Step 1: In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt. Set aside.
Step 2: In a large bowl, using an electric mixer, cream together the softened unsalted butter and granulated sugar until light and fluffy, about 2-3 minutes.
Step 3: Beat in the large egg and vanilla extract until well combined, scraping down the sides of the bowl as needed.
Step 4: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix the dough. If using, fold in chocolate chips or chunks.
Step 5: Divide the dough in half, flatten each half into a disc, wrap tightly in plastic wrap, and refrigerate for at least 30 minutes, or up to 2 hours. Chilling is crucial for easy handling and to prevent spreading.
Step 6: Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper.
Step 7: On a lightly floured surface, roll out one disc of chilled dough to about 1/4-inch thickness. Use your favorite cookie cutters to cut out shapes. Carefully transfer the cut cookies to the prepared baking sheets.
Step 8: Bake for 10-12 minutes, or until the edges are set and the centers still look slightly soft. Do not overbake.
Step 9: Let the cookies cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely. Once cooled, they are ready to serve or decorate.