Preheat the oven to 160°C (no fan).
Prepare a 20 cm x 10 cm (8 inch x 4 inch) cake tin. Brush the bottom and edges with margarine and line with baking paper.
Beat the eggs to a fluffy foam, gradually add the sugar, one spoon at a time, mixing each time for a few seconds. At the end add the melted butter, vanilla extract and milk.
In a smaller bowl weigh out the flour, cocoa, baking powder, a pinch of salt and coffee extract. Add to the eggs and gently combine the ingredients.
Add the chopped chocolate and nuts, combine.
Place at the middle rack of the preheated oven. Bake for 50 minutes, until the knife inserted into the dough is dry. Cool before topping with the ganache.