Preheat oven to 350F degrees. Line a cookie sheet with parchment paper or silicone baking mat. Set aside.
In a medium size bowl, mix the softened butter and sugars together with a spoon or fork until creamed. Mix in the egg and vanilla.
In a separate small bowl, mix the flour, cocoa powder, baking soda, and salt. Pour the dry ingredients into the wet ingredients and mix to combine. Fold in 1/4 cup chocolate chips.
Place the dough in the center of the baking sheet and mold into a tall ball using a spoon (see picture above). Dot the top of the cookie with 1 Tablespoon of chocolate chips. Add sprinkles on top if desired. Bake for 14-15 minutes, or up to 16 minutes. The cookie will appear very soft, but will firm up as it cools. Allow to cool completely on baking sheet.