Pour olive oil into the saucepan or soup pot on the stove and turn the heat to medium.
Add onion to the heated olive oil, and sauté until the onion is softened and translucent. This process takes 2-3 minutes.
Add chopped garlic, and sauté for an additional minute until fragrant.
Add the salt, black pepper, and red pepper flakes.
Add half of the beans to the onion and garlic mixture. Mash the beans. (See video.)
Add the chopped escarole to the onion, garlic, and mashed bean mixture, and stir well to incorporate the greens.
Add the remaining beans and broth to the pot, stir well, and bring the mixture up to a boil. Next, turn the heat to medium, cover the pot, and allow the soup to simmer for 10 minutes.
After 10 minutes, turn off the heat. Your soup is ready to serve, and you can ladle it into soup bowls. If you want, you can also grate cheese on top of the soup.
This soup will stay fresh, refrigerated for 3-4 days. Or you can freeze it for up to 3 months.