In 4 1/2- to 5-quart Dutch oven, melt butter over medium-high heat. Cook onion and garlic in butter, stirring occasionally, until onion is tender.
Stir in remaining ingredients except sour cream and cilantro. Heat to boiling; reduce heat to low. Simmer uncovered 2 to 3 minutes, stirring occasionally, until hot.
Top each serving with sour cream; sprinkle with cilantro.