Preheat oven to 325 degrees F/170CPrepare 2 cookie sheets with baking paper
In a microwave-safe bowl, melt the chocolate chips on medium power in 30-second intervals until just melted.
In a medium bowl, combine the flour, cocoa powder, baking powder, and salt. In a large bowl, beat butter, brown sugar and granulated sugar until creamy. Add melted chocolate and mix until combined. Add egg and vanilla extract and mix to combine well.
Add the dry ingredients and mix until blended.
Chill 20 to 30 minutes.
Place ½ cup of the sprinkles onto a plate. Roll the dough between your palms into 1-inch balls, roll into the sprinkles, place onto a prepared cookie sheet 2 inches apart, and bake 12 to 14 minutes.
Cool on the pan for 5 minutes before placing them on a wire rack to cool completely.
Video
Notes
FAQsWhere Do I get the sprinkles you use? I lived in the UK when I made this post (you can get them at most supermarkets there). In the US, I've seen similar on Amazon. Baker's Tips
Some larger-sized sprinkles cause the cookies to flatten and ruin the cookies. For best results, use small size sprinkles (as pictured).
Be sure to start with room temperature ingredients so the butter and egg mix together easier.
Cream the butter and sugar well. Be sure to cream the butter and sugar long enough. Cream until light and fluffy. That said, over-creaming will also affect the baking resulting in a cookie that can collapse.
Check the date on your Baking Powder. Make sure you're using baking powder that's not too old. This can affect how well the cookies rise and bake.
Be careful not to over-mix. Over mixing the cookie dough once the flour is added will also affect the end result of the baking. Only mix until the flour is combined on a lower speed (when in doubt, mix by hand).
Be sure to chill the cookies before baking.The cookie dough will need to chill for several hours before it can be baked. This keeps the cookies from spreading and allows the dough to firm up so that it doesn’t stick to your hands (although it will still be slightly sticky when you go to roll it)
Don’t be shy with the sprinkles. Make sure each cookie is coated well before baking.
Don’tflatten the dough balls once coated and placed onto the baking sheet. They will naturally bake into cookies.
Start with a hot oven. If you don't preheat the oven, the cookies won't crinkle or bake correctly
Bake one batch at a time on the middle rack. You'll get the best possible results when doing so. If you need to bake more than one batch at a time, not only turn the pans but rotate the baking sheets from the top rack to the bottom rack halfway through the baking process to encourage even baking.