For the mashed potato:
Boil the potatoes in salted water and, while still warm, peel and mash them. Place them in a saucepan. Add butter, a pinch of nutmeg and a pinch of salt. Mix with a wooden spoon and stir in the hot milk little by little until you soft and creamy.
Thinly slice the red onions, fry them in a pan with extra virgin olive oil, a pinch of salt and 2 generous tablespoons of sugar. Simmer and add warm water until the onions are soft and golden.
In a small saucepan, pour plenty of extra virgin olive oil. Once hot, put the sage leaves in, after coating them in flour, for a few seconds, until they are golden brown.
In a separate pan, fry the chicken frankfurters in extra virgin olive oil.
Serve by putting mashed onto a plate, topped with caramelised onions and chicken frankfurters, garnish with the fried sage.