Preheat oven to 350°F. Line 2 baking sheets with parchment paper.
Using an electric mixer, beat butter and sugar in large bowl until light and fluffy (about 5 minutes on medium speed). Beat in eggs and peppermint extract.
In a separate bowl, whisk flour, cocoa powder, baking soda, baking powder and salt. Add to mixer bowl and beat until just combined. Stir in chocolate chips.
Form dough into 1-inch balls. Place 2 inches apart on prepared baking sheets.
Bake cookies 6 minutes, then remove them from the oven, bang the pan firmly on the counter and press a few more chocolate chips or chunks into the centers. Continue baking until edges begin to firm but center still appears soft, about 3 more minutes. Cool on baking sheets 5 minutes then transfer cookies to cooling rack.
When you take the cookies out of the oven to add extra chocolate on top, first bang the pan on the counter to deflate them.
Press in chocolate chunks or chips and return the cookies to the oven.
You'll know they are done when the edges are dry and crackly.
As soon as they come out of the oven, use an overturned glass to re-shape the cookies into perfect circles (see video).
Feel free to substitute the chocolate chips for chocolate chunks or better yet, chopped-up mint chocolate bars (dark chocolate only, milk chocolate will scorch).