Warm up a cold winter night with a pot these flavorful beans and vegetables.
Heat oil in a large, heavy saute pan over medium-high heat. Add fennel and onion; cook, stirring occasionally, until tender and edges are brown, about 10 minutes.
Add beans, stock, chopped oregano, 1 teaspoon salt, and 1/4 teaspoon pepper. Cook, stirring occasionally, until liquid has reduced by about half, 3 to 4 minutes. Stir in vinegar and butter; remove from heat. Garnish with oregano leaves.