Grease a ring cake tin (approx. 2 1⁄2 l capacity) and dust with flour. Preheat the oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer).
Separate 3 eggs and chill the egg white. Cream 250 g butter, 350 g sugar, vanilla sugar and 1 pinch of salt with the whisks of the mixer. Stir in buttermilk, 4 eggs, egg yolk and orange peel.
Mix 500 g flour and baking powder and stir into the egg-sugar mixture in portions. Smooth the dough in the tin and bake in a hot oven for 1-1 1⁄4 hours.
Remove the cake and sprinkle with approx. 3 tbsp. orange juice. Leave to cool in the mould for about 30 minutes. Turn out onto a cake rack and sprinkle with the remaining juice. Let it cool down.
Beat the egg whites until stiff, adding 150 g sugar at the end. Stir until the sugar has dissolved and the mixture is shiny. Spread the egg whites loosely over the cake. Carefully scorch with a kitchen gas burner.