Separate eggs. Beat the egg whites and 2 tablespoons of cold water with the whisks of the hand mixer until stiff. Finally, add 100 g sugar and salt. Beat the egg yolks one after the other. Mix flour, 2 tbsp. cocoa and baking powder, sieve onto the egg foam and fold in carefully
Put the sponge mixture on a baking tray (32 x 39 cm) lined with baking paper, smooth it down. Bake in the preheated oven, middle shelf (electric oven: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 10 minutes. Turn the sponge cake onto a tea towel sprinkled with a little sugar. Carefully remove the baking paper. Roll the sponge cake plate in the cloth and let it cool down for about 30 minutes
Soak gelatine in cold water. Whip cream and vanilla sugar until stiff. Squeeze the gelatine, dissolve and mix with approx. 2 tbsp. cream. Add the gelatine to the rest of the cream while stirring, spread on the sponge cake, leaving an approx. 1 cm wide rim all around. Roll up the sponge cake from one long side using a tea towel. Chill for about 2 hours.
For the buttercream, mix pudding powder, 5 tablespoons of milk and 50 g of sugar. Bring the remaining milk to the boil, then add the pudding powder while stirring. Bring the pudding to the boil and let it simmer for about 1 minute while stirring. Pour into a bowl and let it cool down, the surface covered with foil (best at room temperature overnight)
Whisk the warm butter with the whisk of the hand mixer until creamy white. Stir in 3 tbsp. cocoa powder. Briefly stir the cooled chocolate pudding (room temperature) until smooth, then slowly stir it into the butter by the spoonful. Remove the sponge roll from the cloth, cut 1/4 of the roll diagonally and place it on the roll as a "branch
Lift the sponge roll onto a plate. Spread the sponge roll evenly with buttercream. Use a fork to draw the grains into the cream and refrigerate for at least 2 hours. Before serving, decorate with sugared cranberries and rosemary if desired
waiting time approx. 4 1/2 hours