Preheat oven, line pan with foil, leaving a good hangover to help with the removal of cake. Grease the sides of pan and the foil.

In a double boiler over hot but not steaming water, melt the chocolate with the butter and coffee, stirring occasionally.
Beat the eggs on high speed for 30 seconds, until foamy.
Gradually add the sugar and continue to beat another 2 minutes, until mixture is light and fluffy.
Reduce speed to low and gradually add the chocolate mixture, mix just until blended.
Stir in the flour by hand, and do not over-beat.
Pour the batter into prepared pan, bake on center rack of the oven.
It should remain slightly moist in the center. Cool on rack for 30 minutes.

Cover tightly and chill for a minimum of 6 hours.
Remove the cover and run a knife around edges to loosen.
Lift from pan using the overhanging foil.
Invert and peel off foil.
Invert again and cut to serve.