Preheat your oven to 350F. Line a baking sheet with parchment paper.

Mix the dry ingredients. Whisk flour, cocoa, baking powder and salt together in a medium bowl, set aside.

Melt the chocolate. In a medium, microwave safe bowl, combine chopped unsweetened, bittersweet and semisweet chocolate. Microwave at 50% for 1 minute, then stir. Continue in 1 minute increments, stirring each time, until the chocolate has melted. Set aside to cool slightly.

Mix the wet ingredients. In a small bowl whisk the eggs and vanilla together. Set aside.

Make the cookie dough. In a stand mixer with a paddle attachment, beat the butter, brown sugar and granulated sugar at medium speed until combined, about 45 seconds. Reduce the speed to low and gradually add the egg mixture.

Mix until incorporated, about 45 seconds. Add the melted chocolate in a steady stream and mix until combined, about 40 seconds, scraping down the sides of the bowl as needed.

With the mixer still running on low, add the dry ingredients and mix until just combined. Do not overbeat. Fold in ¾ cup of M&Ms. Cover the bowl with plastic wrap and let stand at room temperature until consistency is scoopable and fudge-like, about 30 minutes.

Shape the cookies. Working with 2 tablespoons of dough at a time, roll into balls and space about 2 inches apart on prepared baking sheet. (I was able to fit 6 balls onto a sheet.)

Decorate. Use the remaining ¼ cup of M&Ms to decorate the dough by gently pressing 2-3 candies on to the top of each ball. If you are using candy eyes for Halloween cookies add those into the dough as well. With the bottom of a glass or the palm of your hand, slightly press each cookie dough ball so that it is just a bit flattened. (Not by much, just a touch.)

Cover remaining dough with plastic wrap so that you can bake the cookies in batches.

Bake the cookies. Bake until the edges of the cookies have begun to set but the centers are still very soft, about 10 minutes, rotating the pans halfway through baking.

Cool. Let cookies cool on the sheet for about 5 minutes before transferring to a rack with a spatula to finish cooling. The cookies will firm up during the cooling process.