These are a twist on a recipe from one of my mother's favorite cookbooks, The Everyday Gourmet. I've added espresso powder and subtracted the nuts, because that's how I roll. (Oh, and, Jane? That's my mom!) —queenie_nyc
Pre-heat the oven to 350°F. Grease a 13x9 baking pan and set aside.
Melt the butter and chocolate together in a double-boiler set over very low heat. Allow to cool slightly.
Beat the eggs and sugar together until pale yellow. Add the cooled chocolate mixture and beat until well-combined. Mix in the flour, espresso powder, baking powder and salt and stir until combined. Fold in the chocolate chips and vanilla.
Pour the batter into the prepared pan and back 25-30 minutes, until just set in the center. Allow to cool on a rack before cutting.