Preheat oven to 210C, line a 12-muffin pan with cup cake liners.
Melt butter and choc in microwave and check intermittently.
Set aside to cool.
Meanwhile, whisk eggs and sugar till ribbon stage.
Stir in butter and chocolate mixture.
Fold in plain flour, orange liquer and cocoa powder.
Cool mixture in the fridge before baking or bake immediately. (I prefer to bake later)
Bake in a medium to high rack for 6-7 minutes.
Remove from oven and best served immediately. These actually taste good served cooled as well.
*Important notes: if you want a thicker cake layer and less lava, lower the temperature by 10C and increase the baking time by 1 minute. If you want a thinner and more hardened outer layer and more lava, add 2 Tbsp of milk to the batter, do 6 minutes at 230C. Watch and do not let it burn!