Spaghetti with Lobster in Light Tomato Sauce

I TRIED this dish for the first time in a taverna, in a remote seaside village on Kythera about six years ago. The cook would set aside a little of the tasty fish stock he used in the many fish soups served at lunch. At dinner, if he had taken a liking to you, he would offer you his signature dish, made with pasta which he cooked in the reserved stock. He stewed the lobster separately with onions and tomatoes and mixed it with the pasta at the last moment. It was delicious, but difficult to