Chop the onion and garlic with half the pancetta cubes and sauté with the butter and oil until the onions become transperant. Add the Arborio rice to the pan and stir for 2 minutes before adding in the white wine. In a small pan, bring the stock to the boil and add to the rice. Continue to cook on a low heat until the liquid is all absorbed. Cut the artichokes into small pieces together with the remaining pancetta and add to the cooked rice. Stir together well, remove off the heat and stir in the lemon juice, thyme and Mascarpone. Cook the spring roll pastry sheets till golden and crispy and flake to garnish the risotto.