1In a large saucepan, heat 2 tablespoons olive oil over high heat. Add the shrimp, season with salt and cook, stirring, until pink and firm, 2 to 3 minutes. Transfer the shrimp to a medium bowl and let cool slightly. Peel the shrimp and transfer to a clean bowl. Return the shells to the pot. Add 8 cups water and 3 sprigs thyme, bring to a boil and cook over medium heat for 2 minutes. Strain the broth into a large glass measuring cup, pressing on the shells to extract any juices; discard shells and thyme. Set aside broth.
2Add the onion, celery and remaining olive oil to the pot; season with salt and a pinch of cayenne. Cook over medium heat, stirring occasionally, until the vegetables are softened, about 5 minutes. Stir in the tomato paste then the wine. Bring to a boil and cook until the liquid is almost evaporated. Add the shrimp, broth and rice. Bring to a simmer and cook over low heat, skimming occasionally, until the rice is cooked, about 1 hour.
3Remove 6 of the shrimp and slice in half lengthwise; reserve. In a blender, puree the soup with the remaining shrimp in batches; return to the pot. Add the heavy cream and bring to a simmer. Cook over medium heat for 5 minutes. Season with more salt and cayenne. Ladle the bisque into bowls; garnish with reserved shrimp and leaves of remaining thyme.