Place the sweet potatoes in a pan of cold water and bring to the boil. Simmer until tender, for about 20 minutes. Remove from the heat, drain then mash with 100g of butter and season with salt and freshly ground black pepper.Keep covered and warm.
Preheat oven to 200°C/400ºF/Gas Mark 4. Cut each pork chop horizontally almost through making a pocket for stuffing.
Melt 50g of butter in a small pan over medium heat. Add the onion, garlic and mushroom and sauté for 5 minutes until coloured. Add thebreadcrumbs and rosemary and continue to sauté for 2-3 minutes. Transfer to a bowl to cool.
Mix the cheese into the breadcrumb mixture; season with salt and pepper. Insert stuffing into pockets in pork, dividing equally. Skewer pockets closed with toothpicks if necessary.
Heat a tbsp of oil in an ovenproof pan over high heat. Add pork and sauté until caramelised or browned on both side, about 2 minutes per side. Place pan in oven. Cook for about 10-15 minutes.