Chocolate Refrigerator Cake

250 grams good-quality dark chocolate [min. 70% cocoa solids], roughly chopped
250 grams plain biscuits
100 grams soft butter

150 grams caster sugar
3 large eggs
2 tablespoons unsweetened cocoa powder

Crush biscuits.  Melt chocolate in a bowl over boiling water.  Allow to cool slightly
Beat butter and sugar, then add the eggs one at a  time and continue beating.  Add cocoa to the melted chocolate and stir until combined, then add this to the egg mixture.  Mix until smooth, then add the crushed biscuits and pour into lined cake tin and place in fridge until set.