Preheat the oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper.
In a large bowl, whisk the Greek yogurt, eggs, monk fruit sweetener, melted butter, vanilla and instant coffee until smooth and the coffee has dissolved. The coffee will not taste like coffee, it simply makes the chocolate flavor deeper.
Add the cocoa powder, flour, baking powder and salt. Fold gently just until no dry streaks remain. Overmixing makes these cakey instead of fudgy.
Fold in the chocolate chips, then spread the batter evenly into the pan and smooth the top.
Bake for 20-24 minutes, until the edges are set and the center is just barely firm. A toothpick should come out with moist crumbs.
Cool completely in the pan before cutting into 16 squares. They taste even richer the next day, so store leftovers covered in the fridge.
