Preheat oven to 350ºF. Prepare a baking sheet by lining it with parchment paper.
Combine the flour, baking powder, salt, and cocoa together in a mixing bowl and set aside.
In a separate large mixing bowl, whisk the butter and sugar together.
Then, whisk in the egg, vanilla, and peppermint extract.
Stir in the flour and cocoa mixture until just combined.
Using a small cookie scoop, scoop the cookie dough and place it about 2 inches apart onto the prepared baking sheet.
Press three M&Ms into the top of each.
Bake in a preheated oven for 10 minutes until the cookies are mostly set, but they look a little under-baked in the middle. These are brownie-type cookies, so you don't want them to be too dry.
Allow the cookies to cool on the baking sheet while they finish setting up.