Preheat the oven at 175 degrees Celsius
Place a baking paper in a baking form with removable edges.
Melt the butter and the chocolate in a casserole. Remove the casserole from the stow and let it cool down for a while.
Mix the eggs with the sugar with an electrical mixer. Add the flour, vanilla flower, cacao powder and mix well.
Add the chocolate and butter mixer and stir together.
Pour the batter in the baking form and place in the oven for 20 minutes.
Whip half the sugar and the egg whites to a hard foam. While stirring gently add the rest of the sugar.
Melt the chocolate and add it gently in the mixture.
Place evenly the meringue on top of the cake and place in the oven for another 5 minutes.
Take out the cake and let it cool down before serving it.