Heat 2 tablespoons oil in a large pot over medium heat. Add onion and cook, stirring often, until softened, about 5 minutes. Add garlic and 1 teaspoon each sage and thyme; cook until fragrant, about 1 minute. Stir in cauliflower, broth, beans, pepper and salt. Bring to a boil. Reduce heat to maintain a simmer, cover and cook until the cauliflower is very tender, 15 to 20 minutes.