Step 1

Heat 2 Tbsp. extra-virgin olive oil or vegetable oil in a large Dutch oven or other heavy pot over medium-high. Add 2 large white onions, cut through root ends into 1"-thick wedges, sprinkle with 1 Tbsp. Diamond Crystal or 1¾ tsp. Morton kosher salt, and cook, undisturbed, until golden brown underneath, about 5 minutes. Turn onions over and cook until golden brown on other side, about 5 minutes.

Step 2

Add 5 garlic cloves, thinly sliced, 1 tsp. freshly ground black pepper, and 1½ tsp. thyme leaves to pot; stir to combine. Pour in 4 cups low-sodium vegetable broth and ¾ cup seasoned rice vinegar and bring to a simmer, stirring and scraping up browned bits with a wooden spoon. Stir in two 15-oz. cans cannellini (white kidney) beans, rinsed, 8 oz. frozen white pearl onions (about 1½ cups), 1 Tbsp. distilled white vinegar, and 2 cups water. Return to a simmer and cook, stirring occasionally, until beans, white onions, and pearl onions are very tender and flavors have melded, 35–40 minutes. Taste and add more salt if needed.

Step 3

Ladle beans into bowls; top with more thyme. Serve with slices of crusty country-style bread, toasted for dipping.Do Ahead: Beans can be made 1 day ahead. Let cool; cover and chill.