Cook the pasta according to packet instructions, then drain, keeping a cupful of the cooking water. Keep the pasta warm, set aside the water.
Meanwhile, thinly slice the onion and finely chop the red pepper. Chop the liver into bite-sized chunks.
Heat the oil in a non-stick pan and gently sauté the onion for about 8 minutes, until it has softened.
Add the red pepper and balsamic vinegar, then sauté for 5 minutes, until the onion has slightly caramelised.
Add the liver pieces, marjoram and stir for 1 minute until the colour of the liver has changed.
Add the sherry or brandy and let it sizzle, then stir for a few seconds to reduce.
Mix the pasta water with the chicken stock cube and pour half of it over the liver.
Reduce it for a couple of minutes, but don’t overcook, otherwise the liver will become rubbery.
Mix in the pasta and parsley, tossing well with a tongue. Add more stock if it’s too dry.
Serve with plenty of freshly ground black pepper, garnished with parsley leaves.