Walnut cake

We spent New Year's Eve in the company of friends. Everybody was asked to bring a dish. I prepared two desserts, with expert help. One of them was a walnut cake. A friend gave me the recipe when we were students. It's a very easy recipe and it always meets with succes.
It's the first thing I baked in my new oven and it came out wonderfully.

For the cake:

4 eggs
200 g sugar
250 g flour
1 tsp baking powder
80 g walnuts, chopped
1 glass sunflower oil

For the topping:

2 eggs
150 g sugar
125 g soft butter
150 g walnuts, chopped + a few whole walnuts for decoration
1 tbsp rum

Beat egg yolks and sugar into a creamy mixture.
Mix baking powder into the flour and add this to the egg yolks.
Add chopped walnuts and oil and mix well.
Beat egg whites and add them to the mixture.
Grease a cake tin and add the mixture.
Bake for 30-40 min at 180° C.

Prepare the topping: mix eggs, sugar and butter into a smooth cream. Then add chopped walnuts and rum.
Let the cake cool, then add the topping on top and/or in the middle.
Decorate with a few whole walnuts.

Notes
The cake was a little dry, maybe 200 g flour is enough.
The topping is a big quantity and very rich, so you might also halve the quantities and only add it on top or only in the middle.