Stir together cocoa powder, sugar, cornstarch and salt in a large microwave safe bowl. Gradually add milk and whisk till no lumps exist.
Place the bowl in a microwave at full power for 8-10 minutes. Pause microwave every 2 minutes to stir the mixture. After 8 minutes, the pudding should have thickened.
While its still hot, whisk in chopped chocolate, butter and vanilla extract till pudding is smooth.
Pour pudding mixture into individual dishes. To avoid a skin forming, place a cling film wrap directly on the surface and refrigerate for up to 2 hours. Garnish with roasted almonds, strawberries, cherries or whipped cream. Or all of them.