Preheat the oven to 200°C.
Melt 100g butter in a saucepan and stir in 250ml stock.
Combine chopped ham, bread, pancetta, 30g parsley, shallots, and lemon zest in a bowl with seasoning.
Mix the dry ingredients with the liquid and soak for 20 minutes.
Loosen the skin of the chicken breasts from the opening to the wing bone.
Slide two whole ham slices under the skin on each side of the breast.
Insert 5 sage leaves under the skin on each side of the breast.
Squeeze the stuffing dry and place it inside the chicken cavity.
Pierce the chicken, rub with olive oil, and season with salt and pepper.
Roast the chicken breast-side down in a tray for 60 minutes.
Turn the chicken over and roast for 20 minutes until golden and cooked through.
Boil potatoes for 20 minutes, drain, and mix with remaining parsley.
Simmer 500ml stock in the roasting tray for 5 minutes to reduce fat into a sauce.
Sauté onion and sweetcorn in 50g butter for 5 minutes until soft.
Stir in thyme and mash the sweetcorn until it becomes creamy.
Carve the chicken and serve with potatoes, corn, and reduced sauce.