In a stockpot or large saucepan, heat the olive oil over medium heat. Add the chopped onion, garlic, carrot, and celery. Sauté for about 5 minutes or until the vegetables are softened and fragrant.
Stir in the tomato paste and cook for an additional 2 minutes to incorporate the flavors.
Pour in the white wine, scraping the bottom of the pot to deglaze and incorporate any browned bits, and let it simmer for about 5 minutes.
Add the seafood stock, bay leaf, and dried thyme to the pot. Bring the mixture to a boil, then reduce the heat to low and let it simmer for 15 minutes.
Add the shrimp to the pot and cook for 3-5 minutes, or until they are opaque and cooked through. Remove the bay leaf from the soup.
Using an immersion blender, blend the soup until smooth. If using a regular blender, allow the soup to cool slightly before blending in batches.
Strain the bisque through a fine mesh sieve for an ultra-smooth texture, if desired.
Return the bisque to the pot and stir in the heavy cream and sherry (if using). Season with salt and pepper to taste, and heat gently until warmed through, being careful not to boil.
Ladle the bisque into bowls and garnish with fresh parsley before serving.