Heat oil in heavy large pot over medium heat. Add onion, garlic, and thyme; saute until onion is golden, about 8 mins. Add beans, reserved 1 cup of bean liquid, 3-1/2 cups of broth, tomatoes with juice, cumin and hot pepper sauce.
Bring soup to boil; reduce heat to medium-low and simmer (uncovered) until flavors blend and soup thickens slightly, stirring occasionally, about 20 minutes. Cool slightly.
Working in 2 batches, puree 2-1/2 cups of soup in blender (I used my cuisinart food processor on pulse several times) until smooth. Mix puree back into soup pot.
Brint to simmer. Season to taste with salt and pepper, only if needed. (can be made 1 day ahead. cool slightly, refrigerate uncovered until cold, then cover and keep refrigerated. Bring soup to simmer, thinning with more broth if needed, before serving.
When ready to serve, top with a dollop of sour cream and some shredded cheddar cheese and fresh cilantro (optional) We served this with warm jumbo flaky biscuits and butter!