Preheat oven to 350 degrees.
Line 16 muffin tins with parchment liners
Combine milk & vinegar in small cup & set aside
In large bowl - whisk together flour, brown sugar, cocoa powder, baking powder, baking soda & salt.
Add in mint chips & stir to incorporate
In separate bowl combine milk mixture & eggs- whisk
Add in oil & coffee extract - whisk to combine.
Pour into dry mixture & carefully fold in. Do not over mix.
Scoop by the spoonful into prepared baking tins until the papers are 3/4 full
Bake 23- 25 minutes or until toothpick test is clean.
Let cool in pan & then transfer to wire rack to finish cooling.
Store in airtight container.