1/2 cup chopped tomatoes (fresh or canned) with juices
2 medium-size onions, sliced
2 celery ribs, sliced
2 small carrots, sliced
4 garlic cloves, crushed
4 sprigs fresh thyme
2 dried bay leaves
1 teaspoon whole black peppercorns
1/4 teaspoon fennel seeds
Kosher or sea salt
Split carcasses’ heads; remove head sacs and discard. Place carcasses and shells in a large (6- to 8-quart) pot and add 2 quarts water. Heat to boiling; skim scum from surface. Reduce heat to a gentle boil.
Add wine, tomatoes, onions, celery, carrots, garlic, thyme, bay leaves, peppercorns, and fennel seeds. Cook until liquid is reduced by half. Add water if liquid cooks to below lobster shells.
Season to taste with salt; simmer 15 minutes more. Strain stock. If not using immediately, chill quickly. Cover and refrigerate stock up to 2 days, or freeze for later use.