Remove the husks and silk from the corn and cut off the kernels as close to the cob as possible. You should have about 2 cups of kernels. Set the kernels aside. Break the cobs in half and place in a medium saucepan with 10 cups of water. Cook over low heat for 15 minutes. (The stock should remain at a low boil so it reduces slightly.)
Meanwhile, heat the olive oil and butter in a medium pot or Dutch oven over medium heat. Add the leeks and sauté for 5 to 7 minutes, until tender. Add the rice and stir for one more minute. Add the white wine and simmer over low heat, stirring constantly, until most of the liquid has evaporated. When the stock has been cooking for fifteen minutes, remove the corn cobs and discard, keeping the stock at a simmer as you cook the risotto.
Add the stock to the pot with the leeks and rice, one ladleful at a time, stirring almost constantly and waiting for the stock to be absorbed before adding more. This process should take about 25 minutes.
When the risotto has been cooking for 15 minutes, add the tomatoes, corn, salt and pepper. Continue cooking and adding stock, stirring almost constantly, until the rice is tender but still firm.
When the risotto is done, turn off the heat and stir in the lemon zest, tarragon, Parmesan and lobster meat, reserving a few pieces of lobster meat for serving. Serve immediately, with the reserved lobster pieces on top of each serving.