In a large nonstick skillet over medium heat, cook pork in batches in oil until no longer pink; remove and keep warm.
In the same pan, saute onion until crisp-tender. Add garlic; cook 1 minute longer. Add the broth, vegetables, vinegar, sugar, tarragon and salt; bring to a boil. Reduce heat; cover and simmer for 25-30 minutes or until vegetables are tender.
Combine flour and milk until smooth; gradually stir into vegetable mixture. Bring to a boil; cook and stir for 2 minutes or until thickened. Add pork and heat through. Reduce heat; stir in sour cream just before serving (do not boil).