In a large saucepan over medium heat, melt the butter. Add the onion and celery and sauté until softened, about 5 minutes. Season with the salt and pepper. Add the flour, whisk to create a roux, and cook for 4 minutes (the roux should not brown). Add the stock and Worcestershire and whisk, then add the milk and continue to whisk. Reduce the heat to low, add 1 1/2 cups of the crab meat, and simmer for 20 minutes. Stir in the sherry and simmer for 5 minutes longer. Serve in wide, shallow bowls. Garnish with the remaining crab meat, roe or egg yolk, and dust with paprika.