How to Make It
In a large pot, heat 1 tablespoon of the olive oil. Add the sausage and cook over moderately high heat, breaking up the clumps, until browned, 5 to 7 minutes. Transfer the sausage to a paper towel-lined plate.
Add the remaining 2 tablespoons of olive oil to the pot along with the potatoes, shallots and garlic. Cook over moderate heat, stirring, until the shallots are softened, about 3 minutes. Add the spinach and kale, season with salt and pepper and cook, stirring, until wilted. Add the tomatoes and their juices, the broth and the basil sprigs and bring to a boil. Partially cover and simmer until the greens and potatoes are tender and the soup is thickened, about 25 minutes.
Discard the basil sprigs. Stir in the escarole and sausage and season with salt and pepper. Ladle the soup into bowls, garnish with chopped basil and serve.