To a large mixing bowl, add your butter and white sugar and beat them together with a mixer till creamy. Add your vanilla and egg and briefly blend in.

To the same bowl, add your flour, baking powder and salt. Add your cocoa powder through a fine mesh strainer. Stir together till everything is combined and you have a thick, smooth cookie dough batter.

Place a large piece of saran wrap on your counter and put your cookie dough in the middle in one ball. Gently push your dough into a flat, disc-like shape (so it's easy to roll out later). Wrap the saran wrap around the dough till it's covered entirely. Place in the fridge and chill for at least 2 hours.

After 2 hours, remove your dough from the fridge. Preheat your oven to 350. Spray two pans with non-stick spray (or line with parchment paper).

Using a large spot on your counters, sprinkle flour across the tops so your dough won't stick. Unwrap your dough and place it on the counter. Sprinkle a little more flour across the top of the dough, to prevent it from sticking to your rolling pin.

Roll your dough out to about 1/4 inch in thickness, all around. Continue to sprinkle a little more flour on top so it doesn't get too sticky.

Using a cookie cutter, cut the dough into shapes. Use a thin spatula to remove the cookie cutouts and place them on your pans. I recommend placing similarly sized cookies on the same pan, so the cookies bake evenly.

Bake for 7-12 minutes (depending on the size of your cookies), or till the edges are set and the cookies are cooked through. Smaller cookies will take about 7-8 minutes, medium cookies about 8-10, and large cookies about 10-12 minutes.

With the leftover cookie dough, you can push it together (forming another disc) and re-roll it with your rolling pin. Be sure to use flour on your counters again and on top of the dough. Continue till you've cut out as many cookies as you can!

After your cookies have cooled entirely, frost and decorate them.

To a small mixing bowl, add your powdered sugar and cocoa powder and whisk them together till well combined. Add 2 tbsp of water, corn syrup and vanilla and continue to whisk till you have a thick, smooth icing. Add another tbsp of water if necessary.

Spread or pipe onto cookies, add sprinkles, and enjoy!