Place the new potatoes in a saucepan, fill with water and bring to the boil. Turn down the heat and simmer until the potatoes are tender. Drain and set aside.
Heat one tablespoon of oil in two heavy-based frying pans set over a medium heat. Divide the onion between the two pans and fry gently for 10 minutes, or until soft and golden-brown.
Add half the nduja and chilli to each pan and cook for three minutes. Stir in equal amounts of the Serrano ham, cook for a further three minutes.
Add half the potatoes, capers and butter to each pan. Let the potatoes brown - keep turning them every so often with a spatula until crisp all over.
Make two holes in the mixture in each pan. Crack two eggs in each hole, cover with a lid and cook for three minutes until set.
Meanwhile, toast the bread on a griddle pan until crisp.
Spoon the hash onto four plates, giving each person two eggs, and sprinkle over the parsley. Serve with the toast and chilli sauce on the side.