Preheat oven to 400 degrees F. Butter and flour 4 (4-ounce) ramekins. Combine chocolate and butter in a double boiler and melt. Stir in cocoa powder. In a bowl beat egg whites on medium speed until soft peaks form. Increase speed to high and gradually add sugar. Beat whites until stiff and glossy, but not dry. Whisk 1/4 of egg white mixture into chocolate, to temper. Fold in remaining whites. Fill ramekins 2/3 full and bake until top is slightly firm but still soft in the very center, about 6 to 8 minutes.
Mixed berry coulis:
Combine raspberries, blueberries, strawberries, sugar and lemon juice in a saucepan and heat until fruit is softened. Remove from heat and puree in food processor until smooth. Strain through a sieve and stir in liqueur or orange juice. Chill.