Bring the 4 cups of water to a boil and add the lobster tails.

Boil for 4 minutes, then take out the lobster and plunge it into iced water to stop it cooking any further.

Remove the lobster meat from the shells, dice it and place in refrigerator unti you are ready to make the risotto.

Put the lobster shells back into the boiling water and add the onion, carrot, celery, tomato, bay leaf, plus salt and pepper to taste. Simmer the stock for 20 minutes.

Remove from the heat and strain, then return the lobster stock to a low heat, ready to use for the risotto.

Heat the olive oil in a large skillet and cook the shallots and garlic for a couple of minutes, until softened.

Stir in the Arborio rice and cook for another couple of minutes, then pour in the white wine. Cook for a minute, stirring constantly.

Pour in just under half of the lobster stock and cook for 3 to 5 minutes, stirring occasionally, until most of the liquid has been absorbed by the rice.

Add the rest of the lobster stock one ladle-full at a time, so that the rice slowly absorbs the liquid. This should take around 20 minutes total and the rice should look slightly translucent, with an al dente texture and a just visible 'core' at the center.

Put in the reserved lobster meat, plus the mascarpone cheese, lemon zest, and salt and pepper (to taste).

Stir thoroughly until the ingredients are well mixed and the texture is thick and creamy.

Serve garnished with parmigiano and chives.