Step 1: Prepare the Dough

1. Cream the Butter and Sugar: In a large mixing bowl, use a hand mixer or stand mixer to beat the softened butter and granulated sugar together until light and fluffy (about 2-3 minutes). Scrape down the sides of the bowl as needed.
2. Add the Egg and Vanilla: Beat in the egg and vanilla extract until fully incorporated.

Step 2: Mix the Dry Ingredients

1. In a separate bowl, whisk together the flour, cocoa powder, baking soda, baking powder, and salt.
2. Gradually add the dry ingredients to the wet ingredients, mixing on low speed until a dough forms. Be careful not to overmix.

Step 3: Chill the Dough

1. Divide the dough into two portions and flatten each into a disc. Wrap the discs in plastic wrap and refrigerate for at least 30 minutes. This helps the dough firm up, making it easier to roll and cut.

Step 4: Preheat the Oven and Prepare the Baking Sheets

1. Preheat your oven to 350°F (175°C).
2. Line two baking sheets with parchment paper or silicone baking mats.

Step 5: Shape the Cookies

Option 1: Rolled Cookies

1. Lightly flour a clean work surface and rolling pin. Roll out one portion of dough to about ¼-inch thickness.
2. Use cookie cutters to cut out shapes, transferring them to the prepared baking sheets. Re-roll scraps as needed.

Option 2: Drop Cookies

1. Scoop tablespoon-sized portions of dough and roll them into balls.
2. Roll each ball in granulated sugar or sparkling sugar, then place them on the baking sheet, spacing them about 2 inches apart.

Step 6: Bake the Cookies

1. Bake the cookies in the preheated oven for 10-12 minutes, or until the edges are set. The centers may look slightly underdone, but they’ll firm up as the cookies cool.
2. Remove the baking sheets from the oven and let the cookies cool for 5 minutes before transferring them to a wire rack to cool completely.

Step 7: Decorate (Optional)

1. Once the cookies are completely cool, decorate them with royal icing, melted chocolate, or sprinkles. Let the decorations set before serving or storing.