Preheat the oven to 350°F (175°C). Line baking sheets with parchment paper.
In a large bowl, cream together the softened butter and both sugars until light and fluffy, about 3–4 minutes.
Beat in the eggs one at a time, then mix in the vanilla and peppermint extracts until fully combined.
In a separate bowl, whisk together the flour, cocoa powder, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, mixing on low speed until just incorporated.
Fold in the chocolate chips using a spatula until evenly distributed throughout the dough.
Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart.
Bake for 10–12 minutes, or until the edges are set but the centers still look slightly soft. The cookies will firm up as they cool.
Allow cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
Notes
These cookies stay soft and chewy when stored in an airtight container at room temperature for up to 5 days.