Preheat the oven to 375°F.
Place the fish, potatoes, carrots, onion, olive oil, sherry wine, Worcestershire sauce, bay leaf, salt, pepper, dill, and celery seed in a large Dutch oven or ovenproof pot or casserole, and gently stir to combine.
Cover and bake until the fish is cooked and the vegetables are tender, about 1 hour. Remove from oven and set aside.
About 15 minutes before the fish is done, prepare your “cream” sauce. Cook the pancetta in a medium saucepan over medium heat, stirring frequently, until crispy, about 5 minutes.
Add the butter and heat until it melts. Add the flour and whisk constantly until smooth, about 2 minutes. Whisk the milk and broth slowly into the flour mixture. Raise the heat and bring to a low boil, stirring constantly. Reduce the heat and continue to simmer and stir gently until the mixture thickens, about 3 minutes.
Remove from the heat, and whisk in the sour cream as desired. Add the sauce to the fish mixture and stir gently to combine. Remove the bay leaf. Serve in individual bowls and top with oyster crackers as desired.