Rinse live lobsters under cold water. You can steam or boil them. I prefer steaming. To boil, bring a large pot of salted, water to a boil, quickly submerge the lobsters head first. Cook a one-pound lobster for about 12 minutes. Alternatively, you can steam the lobster for about 7 minutes, over two inches of boiling water, setting the lobster on a rack and covering the pot. Allow to cool, then crack the claws and cut the tail to remove the meat. Cut the meat into bite-size pieces.
In a skillet over medium heat, melt 4 ounces of the butter and add lobster. After minute or two, add the wine, and allow it to evaporate. Remove from heat.
Prepare the Risotto:
In a saucepan over a low flame, add the tomato puree to the stock and keep warm. In a large skillet, over medium heat, sauté the onion in the remaining butter and olive oil until translucent. Add the rice and stir together until opaque and lightly toasted. Add a ladle of the hot stock. Continue to cook and stir (preferably with a fork) until the liquid is almost fully absorbed. As the liquid absorbs, add more stock, a ladle at a time, waiting until almost completely absorbed before adding more. Cook until rice is al dente, about 15 minutes, being careful that the rice remains al dente.
Add the lobster to the skillet with the rice. Mix well and after a minute, remove the skillet from the heat. Serve immediately.