1.Preheat the oven to moderately hot (200°C/180°C fan-forced). Brush the inside of six 1/2-cup (125ml capacity) or four 3/4-cup (180ml capacity) ovenproof dishes with soft butter. Place sugar in one dish, turn dish to coat base and side. Tip the excess sugar into next dish; repeat with all dishes. Place dishes on oven tray.
2.Dissolve coffee in the water. Combine the chocolate, extra butter and dissolved coffee in a large heatproof bowl over a pan of simmering water; stir until melted. Remove bowl from heat; stir in egg yolks.
3.Beat the egg whites in a large bowl with an electric mixer until soft peaks form; gradually add the extra sugar and beat until dissolved.
4.Using a large balloon whisk, gently fold one-third of the egg-white mixture into the chocolate mixture, then gently fold in the remainder of the egg-white mixture.
5.Divide souffle mixture among prepared dishes to fill; level the tops. Bake in a moderately hot oven for about 12 minutes for smaller dishes or 15 minutes for larger dishes, or until souffles are puffed.
6.Meanwhile, to make chocolate sauce, place chocolate in a small heatproof bowl over a pan of simmering water; stir until melted; stir in cream and liqueur.
7.Dust souffles with sifted cocoa and serve immediately with chocolate sauce.