Chop the chocolate coating and melt it with the butter in a water bath.
Beat the eggs with the vanilla and sugar until creamy and stir in the chocolate butter. Sift the flour with the cocoa over it and mix with the espresso. Mix in the pecans.
Preheat the oven to 170°C bottom and top heat. Line a baking pan (about 24×24 cm) with baking paper. Pour the batter into the pan, smooth it out and bake in the oven for about 25 minutes.
Remove from the oven and let cool. Before serving, cut into pieces and sprinkle with cocoa powder according to personal taste.