01 - 
                Add reserved shrimp shells to a saucepan with 4 cups water. Bring to a boil, then reduce heat and simmer for 30 minutes. Strain through a sieve, discard shells, and measure broth, adding water as needed to total 4 cups. Set aside.
              
              
              
                02 - 
                Heat olive oil in a 4-quart Dutch oven over medium heat. Add diced shallots and sauté gently for 3-4 minutes until softened without browning. Add minced garlic and cook for 1 additional minute.
              
              
              
                03 - 
                Stir in cayenne pepper and shrimp. Cook until shrimp turn pink, about 3-4 minutes. Remove 6 shrimp and set aside for garnish. Add brandy and cook 1-2 minutes, then add sherry and cook another 3 minutes.
              
              
              
                04 - 
                In batches, transfer shrimp mixture to a blender and puree until smooth. Exercise caution when blending hot liquids, filling the blender no more than halfway and allowing steam to escape. Return puree to the Dutch oven.
              
              
              
                05 - 
                Melt butter over medium-low heat in the Dutch oven. Whisk in flour and cook for 1 minute. Gradually whisk in heavy cream and milk until mixture is smooth and thickened.
              
              
              
                06 - 
                Add shrimp broth, pureed shrimp mixture, tomato paste, salt, and white pepper. Heat gently, whisking constantly to avoid boiling and curdling. Adjust heat as necessary until hot but not boiling.
              
              
              
                07 - 
                Ladle bisque into bowls, garnish with reserved shrimp and chopped parsley. Drizzle each serving with 1 tablespoon truffle oil.