Sort and wash beans; place in a Dutch oven. Cover with water to 2 inches above beans; bring to a boil, and cook 20 minutes. Remove from heat; drain beans.
Preheat oven to 375°.
Heat oil in pan over medium-low heat. Add onion; sauté 10 minutes. Add beans, broth, and the next 5 ingredients (beans through bay leaf); bring to a boil. Cover and bake at 375° for 1 hour and 15 minutes. Stir in collards, vinegar, and tomatoes. Cover and bake an additional 1 hour or until beans are tender, stirring occasionally. Stir in salt and pepper. Discard bay leaf. Garnish with thyme sprigs, if desired.