Heat the olive oil and butter in a pan over medium high heat until the butter melts. Add the onion and garlic until completely soft and translucent, 10-15 minutes stirring occasionally. Stir in the parsley and cook for 1 minute.
Roughly cut the avocado and add it to the onion mixture. Add the chicken broth, salt, pepper, lemon juice and hot sauce. Cook over medium heat for 10 minutes.
Working in batches if necessary, place the soup in a blender or food processor and puree until smooth. Taste for seasoning.
Serve hot with a dollop of sour cream. Or serve cold.