Peel and finely grate the sweet potatoes. Coarsely chop the nuts. Cream 200 g butter, sugar, salt and vanilla sugar with the whisk of the hand mixer. Stir in eggs one after the other. Mix flour and baking powder and stir in alternately with the milk.
Stir in sweet potatoes and nuts. Pour into a greased springform pan (26 cm Ø) sprinkled with flour and bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 45 minutes.
Remove and let it cool down.
Wash the orange, rub dry and grate the peel. Cream 50 g butter and icing sugar. Add cream cheese, cream and half the orange peel. Whip the mixture until creamy.
Carefully remove the cake from the tin and lift it onto a cake plate. Spread Frosting loosely on top and decorate with the remaining orange peel.