Preheat oven to 350°F. Line an 8x8 square pan with parchment paper and butter generously.
In a microwavable bowl, melt butter and ¾ cup chocolate chips until melted and smooth. Stir in 30 second intervals. Stir in boiling water, sugar, vanilla and espresso until combined. Stir in the yogurt.
In another small bowl, sift together the flour, cocoa powder, baking powder and salt. Add the dry ingredients to the wet ingredients and mix until just combined and then add the remaining chocolate chips.
Spread evenly into the pan. Bake for 25-30 minutes. A cake tester should come up with a couple of crumbs. Let cool and then cut into 9 squares.
Grease and line your pan with parchment paper so you can easily get the brownies out.