In a medium mixing bowl melt the butter in the microwave. Add in the eggs, vanilla and caster sugar. Mix well.
Sift in the flour and cocoa powder. Using a large spoon gently combine the flour, cocoa powder and coffee powder into the egg mixture until just combined. Be careful to not over mix.
Pour in the chocolate chips and stir once or twice to mix the chocolate chips throughout the batter. Spread the brownie mix evenly into the tin and bake for about 18 minutes, until the top of the brownie is set and the inside is still slightly fudgy. Let the brownies cool in the pan for about 30 minutes before using a sharp knife to cut into 16 squares.
Notes
Don't over mix the batter once you add in the flour. When mixing in the chocolate chips a couple of gentle stirs will do.
Best to under bake these brownies ever so slightly. They keep cooking as they cool in the hot tin. This recipe timing takes that into account.
Wait until the brownies have cooled before removing from the tin and use a sharp knife to slice them.