Preheat the oven to 350 degrees and line two baking sheets with parchment paper.
In a medium bowl, whisk the flour, black cocoa powder, baking powder, baking soda and salt together.
1 ¼ cups (156 g) all-purpose flour, spooned and leveled, 5 tablespoon (35 g) black cocoa powder, ½ teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon salt
Add the softened, unsalted butter, light brown sugar, and granulated sugar to a large bowl. Cream the butter and sugars together with an electric mixer for two minutes, or until light and fluffy. (You can also use a stand mixer with a paddle attachment.)
¾ cup (168 g) unsalted butter, softened, ¾ cup (165 g) light brown sugar, packed, ¼ cup (50 g) granulated white sugar
Add in the egg yolks and vanilla and mix on medium speed for two minutes, or until the mixture is pale in color and fluffy.
2 egg yolks, at room temperature, 1 teaspoon vanilla extract
Add the dry ingredients to the wet ingredients and mix on low speed just until combined.
Add in the M&Ms and Halloween sprinkles and gently fold them into the cookie dough with a rubber spatula.
¾ cup (170 g) Halloween M&M's, 3 tablespoon (36 g) Halloween jimmies
Scoop the dough into 17 balls using a 2-tablespoon capacity cookie scoop. Arrange the dough balls two inches apart on the prepared baking sheets lined with parchment paper. Add extra M&Ms, candy eyeballs and sprinkles on the sides and center of the cookie dough balls.
candy eyeballs for decoration, extra Halloween M&Ms and jimmies for decoration
Bake the cookies for 10-11 minutes.
Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to completely cool. (Some of the eyeballs may melt while baking. I had to swap them out for new ones after baking.)(When the cookies are straight out of the oven, scoot a large circular cookie cutter around them to give them a perfect circular shape.)