Place the butter and unsweetened chocolate in a microwave-safe bowl. Using the lowest heat setting, melt the butter and chocolate in 30-second intervals, stirring until smooth.
In a mixing bowl, whisk the eggs with the sugar, ground coffee, and vanilla. Whisk in the chocolate mixture. Sift the flour, cocoa powder, and baking powder over the batter in the bowl. Fold a few times, add 1/4 cup of the chocolate chips, and fold until well mixed. Pour the batter into the prepared pan and scatter the remaining 1/4 cup chocolate chips evenly over the top.