Boil the lobsters in a large pot of salted water until the shells turn bright red and the meat is opaque.
Remove the lobster meat from the shells, chop it into chunks, and set aside. Keep the shells for later.
In a large soup pot, melt the butter over medium heat. Add onions, carrots, celery, and garlic. Sauté until the vegetables are softened.
Stir in the tomato paste and cook for a couple of minutes until it's well incorporated.
Pour in the brandy or cognac, stirring to deglaze the pot and release any flavorful bits stuck to the bottom.
Add the fish or seafood stock and the reserved lobster shells. Bring it to a simmer and let it cook for about 20-30 minutes to infuse the flavors.
Remove the lobster shells and discard. Use an immersion blender to blend the soup until smooth or you can transfer the soup to a blender in batches and blend until smooth.
Return the soup to low heat, stir in the heavy cream, and add the chopped lobster meat. Simmer for an additional 10 minutes until the lobster is heated through.
Season with salt and pepper to taste. Ladle the bisque into bowls, garnish with fresh parsley, and serve hot.