100g dark cooking chocolate (as dark as you like)
Optional - 1 tsp whisky or orange liquor
Melt together butter and chocolate until they just come together, (I use the microwave)
Add egg yolks and stir together (add any liquor at this stage)
Whip egg whites until stiff peaks form
Fold egg whites into chocolate mixture, folding gently until just combined.
Divide into 4 small serving dishes (very small as these are quite rich)
Refridgerate until firm about 4 hours or overnight