Step 1: Prepare the Lobster Remove the lobster meat from the shells. Use kitchen shears to cut down the back of the shells and pull the meat out. Chop the raw meat into bite-sized pieces and set them aside in the refrigerator. Keep the empty shells, as they will provide the main flavor for your broth.
Step 2: Sauté the Aromatics In a large pot or Dutch oven, melt 2 tablespoons of butter over medium heat. Add the chopped onion, carrot, and celery. Sauté the vegetables for about 5 to 7 minutes until they are soft and the onions are translucent. Add the minced garlic and cook for another minute until fragrant.
Step 3: Build the Flavor Base Stir in the tomato paste and cook for 2 minutes. This helps caramelize the paste and deepens the color of the soup. Sprinkle the flour over the vegetables and stir constantly for 1 minute to cook out the raw flour taste. This will act as the thickening agent for your bisque.
Step 4: Deglaze and Simmer Slowly pour in the dry sherry while scraping the bottom of the pot to release any browned bits. Once the liquid has reduced slightly, whisk in the seafood stock. Add the lobster shells, thyme, and bay leaf back into the pot. Bring the mixture to a gentle boil, then reduce the heat and simmer uncovered for 20 minutes.
Step 5: Strain and Blend Remove the lobster shells, thyme sprig, and bay leaf and discard them. Using an immersion blender, blend the soup until it is completely smooth. If you want an even silkier texture, pour the blended soup through a fine-mesh sieve into a clean pot.
Step 6: Finish with Cream and Lobster Stir in the heavy cream and cayenne pepper. Bring the soup back to a low simmer. Add the reserved lobster meat to the pot and cook for 3 to 5 minutes until the lobster is opaque and tender. Season with salt and pepper to taste.