Preheat the Oven:

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

Cream the Butter and Sugars:

In a large mixing bowl, beat together the softened butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes.

Add the Egg and Vanilla:

Beat in the egg and vanilla extract until well combined.

Combine the Dry Ingredients:

In a separate bowl, whisk together the flour, cocoa powder, baking soda, baking powder, and salt.

Mix the Wet and Dry Ingredients:

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Be careful not to overmix.

Fold in the Chocolate Chips and Sprinkles:

Gently fold in the chocolate chips (if using) and 1/4 cup of rainbow sprinkles.

Shape the Cookies:

Use a cookie scoop or spoon to drop tablespoon-sized balls of dough onto the prepared baking sheets, spacing them about 2 inches apart. Gently press a few more sprinkles onto the tops of each cookie for a festive touch.

Bake:

Bake in the preheated oven for 10-12 minutes, or until the edges are set but the centers are still slightly soft. The cookies will continue to firm up as they cool.