Steam or boil the potatoes for 8–10 minutes, or until tender when pierced with the point of a knife. Drain and return to the pan. Stir over medium heat, then mash. Set aside to cool.
Melt the butter in a frying pan, add the onion and garlic and stir over medium heat for 5 minutes, or until soft. Add the capsicum and cook, stirring, for 5 minute