In a big saucepan, heat the oil and butter over medium-high. Fry livers for about 5 minutes, or until golden but still pink inside. Remove from pan and set aside.
In the same saucepan, sauté onion, garlic and peri-peri spice for about 5 minutes, or until tender. Season with salt and pepper. Add tomato puree, cream and sweet chilli sauce, and bring to the boil.
Meanwhile, cook the shells pasta as per packet instructions. Drain.
Add the livers to the sauce and heat through. Serve with the pasta and sprinkled with parsley.