Melt the butter over medium heat in a small saucepan. Add chocolate chips, remove from heat and stir until chocolate is melted with residual heat.
Let cool for about 15 minutes. Meanwhile, beat the eggs, salt, vanilla and sugar together in a large bowl using an electric mixer for about 3 minutes or until light and slightly thickened. Beat in the espresso/water, followed by the melted chocolate chip butter mixture.
Mix together the flour and the cocoa, then add to batter and stir until absorbed. Stir in the chopped mint chocolate. Chill for 1 ½ hours or until dough is thick enough to shape into balls
Heat the oven to 350 degrees F. Line a couple of cookie sheets with parchment paper. Scoop dough up by well-rounded tablespoons and shape into 1 ½ inch balls. Bake for 9-12 minutes. Let cool. Dust with powdered sugar IF YOU FEEL LIKE IT. No need. I only did it for the photo.
Not sure of the yield yet because I haven’t baked them all, but I think it will be around 16 18 cookies.