Take 8 chocolate cubes (from the normal chocolate) and freeze them for about 3 hrs.
Brush the insides of 8 ramekins (should be 7.5 cm in diameter and 5 cm high) with the melted butter. Dust with the cocoa, tapping out the excesses. Put the ramekins in the freezer.
Place the remaining chocolate, cocoa and cream in a saucepan over a gentle heat until the chocolate is melted and the mixture is smooth. Let cool slightly then beat in the egg yolks and the brandy (or whisky).
Whisk the egg whites with the cream of tartar and a pinch of salt until stiff. Using a large spoon fold the egg whites into the chocolate mixture until smooth.
Pre-heat a baking sheet in the oven at 230 degrees. meanwhile take out the frozen chocolate cubes and the ramekins from the freezer.
Half fill the ramekins wih the souffle' mixture. Place a frozen chocolate cube in the middle and cover with the remaining souffle' mixture.
Cook the souffles for about 8-10 min or until well risen and firm to the touch.