Let the egg yolks stand for some time after beating them. And then whisk with oil and vanilla.
Take a bowl and mix cocoa with water to make a smooth mixture. Cool this mixture for 15 minutes.
In another bowl, mix salt, flour, sugar, and baking powder. Mix all three mixtures now and beat the resulting batter with an electric beater properly.
Now in a separate container, beat the egg whites with the tarter cream. And then gradually add it to the egg yolk mixture by making folds.
Grease the baking pan and gradually spoon the mixture in it evenly or you can also pour it in folds.
Bake your cake sponge at 350 degrees for about an hour and then invert it into a serving plate.
For Icing, in a pan melt the butter and then add confectioner's sugar in it. Also put in chocolate, vanilla, and water.
Pour this chocolate mixture over the cake sponge. Sprinkle the crushed nuts at the top layer of your cake.