Preheat your oven to 340 F. Cut the butter into small dice

Chop the walnuts in the bowl fitted with the metal blade for 30 seconds. Add the sugar, flour, eggs, salt, rum, and butter. Blend for 2 minutes.

While the machine is still running, add the baking powder via the opening. Blend for a further 10 seconds.

Pour the mixture into a well-buttered pan.

Bake for about 30 minutes. To check that the cake is cooked, insert the tip of a knife. It should come out clean.

Allow to cool in the oven with the door ajar.