For the cake, grease the springform pan with butter. Separate the eggs. Beat the egg yolks and sugar until fluffy. Melt the butter and stir into the egg yolk mixture. Sift the flour over and fold in. Beat the egg whites with a pinch of salt until stiff. Fold one third of the egg whites gently into the batter then fold in the remaining egg whites. Pour the batter into the prepared pan. Bake in preheated 180°C (approximately 350°F) oven for 35 minutes. Cool on a wire rack.
For the cream, beat the cream until stiff, gradually adding the sugar. Dissolve gelatin over low heat and stir into the whipped cream. Stir in walnut liqueur. Refrigerate for 30 minutes. Cut the cake crosswise into 2 layers. Drizzle the bottom layer with 2 to 3 tablespoons liqueur and spread with half of the cream. Top with the second cake layer and spread with a generous coating of the remaining cream. Decorate with walnut halves. Melt the chocolate and drizzle over the cake. Refrigerate cake for 5 to 6 hours.