Begin by peeling the shrimp, ensuring to keep the shells for flavor. In a large pot, melt 4 tablespoons of unsalted butter over medium heat. Add the shells and sauté for about 3 minutes until fragrant. Deglaze the pot with ¼ cup of dry sherry, scraping up any brown bits. Pour in 4 cups of water and add the bay leaf, then bring to a simmer for 20-25 minutes, allowing the stock to develop depth.

After simmering, strain the stock through a fine-mesh sieve into a large bowl, discarding the shells and bay leaf. Reserve about 3 cups of this golden shrimp stock, as it serves as the flavorful base for your bisque.

In the same pot, add the remaining 2 tablespoons of butter and heat over medium. Sauté one chopped yellow onion, one chopped carrot, and one chopped celery stalk for about 5-7 minutes, stirring frequently until softened. Incorporate 2 minced garlic cloves and 2 tablespoons of tomato paste, cooking for an additional 2 minutes.

Sprinkle in ¼ cup of all-purpose flour, stirring continuously for about 2 minutes to cook out the raw taste. Gradually whisk in the reserved shrimp stock, and bring the mixture to a gentle simmer. Allow it to cook for 15 minutes, stirring occasionally.

Once simmering, blend the soup using an immersion blender or a stand blender. Return the blended soup to low heat, adding in 1 cup of heavy cream while stirring gently. Taste and season with salt and white pepper.

While the bisque simmers, pat the shrimp dry and season them with a pinch of salt. In a skillet, heat 1 tablespoon of olive oil over medium-high heat. Sear the shrimp for 1-2 minutes on each side.

Ladle the bisque into warm bowls, and garnish with sautéed shrimp on top, swirling in the remaining cream and sprinkling with fresh chives and black pepper. Serve with slices of crusty baguette.