(If using a box mix, skip these instructions and follow the ones on the back of the box)
Preheat oven to 350. Grease an 8x8 baking pan.
Over a double broiler, or in the microwave, melt butter and chocolate together. Once melted, allow to cool about 10 minutes.
Next, add in the sugar, and mix. Add in eggs, one at a time, stirring after each addition. Next, add in vanilla.
Add in espresso powder, salt, baking powder, flour, and cocoa powder. Mix until just combined.
Add in oil and chocolate chips, stir.
Pour into pan, and bake for 25-30 minutes, or until brownies are no longer wet in the middle.
Allow to cool before using a heart-shaped cookie cutter to cut the brownies into hearts (I found that allowing the brownies to chill in the fridge for 60 minutes makes cutting into them easier). Using a medium-sized cookie cutter, I was able to get 9 brownie hearts (if you use a smaller one, you may be able to get 12).