Remove the meat from the shells and set aside.
Melt 2 tablespoons butter in a large saucepan. Add shells and ¼ cup onion and cook over medium heat until fragrant and lightly browned. Add chicken broth and simmer for 10 minutes, covered. Strain, discard shells, and set the lobster broth aside.
Melt remaining butter over medium heat. Add remaining onion, carrots, celery, and garlic and cook until onion is softened. Add white wine and sherry and cook until almost evaporated. Add Worcestershire and Tabasco sauce and cook until almost evaporated.
Stir in the lobster broth (from step 2), thyme, bay leaf, and tomato paste. Simmer uncovered for 15 minutes or until thickened. Remove bay leaf and use an immersion blender to puree until smooth.
Add in cream and simmer until thickened, about 3-5 minutes, stir in lobster meat, and serve immediately. Garnish with chives if desired.
