For the shell stock: In a large saucepan over low heat, add the oil and sweat the prawn shells with the onion, thyme, bay leaves, peppercorns, lemon, and tomato for 2 to 3 minutes. Add the white wine and water and simmer for 45 minutes. Strain and reserve.
For the chowder: In a large saucepan over low heat, add the oil and sweat the onions with the bacon and celery for 5 to 6 minutes. Add the potatoes and sweat for another 5 minutes. Add the thyme, shell stock, and cream and bring to a simmer for 15 to 20 minutes. Add the salmon and season with salt, pepper, and lemon juice. For service, garnish with tarragon and chives.
A viewer or guest of the show, who may not be a professional cook, provided this recipe. It has not been tested for home use.