In a large pot, combine the beans, oil, garlic, sage, and water and place over medium heat. Bring to a boil, reduce the heat to very low, and simmer gently, uncovered, until the beans are tender, 2–3 hours. Do not allow the water to boil and add more water as needed to keep the beans covered by 2 inches of water. The only way to know when the beans are done is to taste them. Add the salt during the last 10 minutes of cooking.

About 30 minutes before the beans are ready, bring a saucepan filled with salted water to a boil over high heat. Add the farro and cook until just tender, about 20 minutes. Drain the farro and reserve.

When the beans are ready, remove from the heat. Transfer half of the beans and bean broth to a clean soup pot. Working in batches if necessary, transfer the remaining beans and bean broth to a blender and puree until smooth. Add the puree to the soup pot and stir to mix well, then stir in the tomato paste, if using.

Place the pot over medium heat and heat, adding water if the soup is too thick and stirring often, until the soup is piping hot. Add the farro and heat through.

To prepare the garnish, in a small skillet or saucepan, warm the oil and herbs over low heat until the herbs are fragrant. Remove from the heat.

Ladle the soup into warmed shallow individual bowls and drizzle an equal amount of the oil-herb mixture over each serving. Serve immediately.