Preheat oven to 375F. Line baking sheets with parchment paper or silicone baking mat.
Melt butter in a large heavy saucepan.
Remove from heat, and stir brown sugar into melted butter.
Let stand 5 minutes.
Add eggs; stir to combine.
Stir in vanilla and peppermint extracts.
Add flour, cocoa powder, baking soda, and salt. Stir until just combined.
Stir in chocolate chips just until incorporated.
Cover and chill for at least 30 minutes. If the dough has been in the fridge for more than 2 hours, let it sit for about 10 minutes before scooping and baking.
Using a medium cookie scoop (1.5 tablespoon), drop scoops of dough 2 inches apart on prepared cookie sheet.
Bake for about 8-10 minutes, or until the edges of the cookies are set. The center will look soft and slightly underdone.
Let cool on cookie sheet for 5 minutes.
Remove to wire rack to finish cooling.
Correctly measuring the ingredients is key. I suggest either weighing the ingredients or aerating the flour (sifting or fluffing) and then scooping and leveling. Packing in too much flour will cause the cookies not to spread or to be dry and crumbly.
Or scant 1/2 teaspoon table salt
I recommend stirring this recipe together by hand rather than using a hand or stand mixer.