Preheat the oven to 180°C. Lay the slices of pancetta on a tray and cook in the oven for 4–5 minutes until crisp. Drain on kitchen paper to absorb any excess fat. Break the pancetta into small pieces. Place the potato purée into a heavy-based pot and add the savoy cabbage, spring onions, shallot and pancetta and warm through over a gentle heat. Season to taste with salt and freshly ground pepper. Just before serving the colcannon, fold through the julienne of parsley.