For the chocolate sheet cake, melt the chocolate with the butter over a bain-marie and allow to cool slightly.Preheat the oven to 160°C hot air (or 180°C top and bottom heat).Beat the eggs with the sugar until foamy and stir in the chocolate-butter mixture. Gradually fold in the grated walnuts and flour. Add the vanilla bean pulp.
Line a baking sheet with parchment paper and spread the chocolate mixture evenly on it. Bake the chocolate sheet cake for about 20 minutes.