If using fresh oysters, shuck them and reserve the juices. If using jarred oysters, strain them through a fine sieve, reserving the water, and rinse the oysters under cold water.

If there are any particularly large oysters, cut them in half.

Melt the butter in a large pot over medium heat, then sprinkle in the flour to make a roux.

Reduce the heat to medium-low and cook the roux, stirring constantly, until it turns golden and the raw flour is cooked, about 2 to 3 minutes.

Add the celery and onions to the roux, and cook for another 2 to 3 minutes until the vegetables soften.

Turn the heat up to medium and keep an eye on the roux to avoid burning.

In a separate pan, mix the oyster juice, hot sauce, milk, and cream, and heat gently over a low flame until just warm.

Slowly add the warm liquids to the roux, whisking constantly to prevent clumping or curdling.

Bring the soup to a slow simmer for about 15 minutes or until heated.

Add the oysters to the soup and cook until they just start curling at the edges, about 2 minutes.

Season with salt and pepper to taste, adjusting for personal preference. Serve hot, garnished with remaining parsley.