Soak black beans in cold water for 1 hour.

Drain the soaked beans.

In a large pot, heat butter or oil over medium heat.

Saute onion, celery, and carrot until softened and golden, about 10 minutes.

Add garlic and thyme and saute for 3 minutes.

Add the drained beans, ham hocks, and water or stock to the pot.

Bring to a simmer, then cover and cook for 1.5 hours, or until beans and meat are tender.

Remove ham hocks from the soup and let cool.

Shred the meat from the hocks, discarding bones, fat, and skin.

Cut the meat into small cubes and reserve.

Puree the soup using an immersion blender or in batches in a regular blender.

Return the pureed soup to the pot and add the reserved meat.

Simmer to heat through.

Season with salt and pepper to taste and add the sherry.

Serve the soup in warmed bowls and garnish with sour cream, hard-cooked egg, or scallions, if desired.