Tuscan Kale Soup with Chorizo

Cook onion in oil in a 5-quart pot over moderate heat, stirring occasionally, until pale golden. Meanwhile, peel potatoes and cut crosswise into thin slices.

Add to onion and cook, stirring occasionally, 4 minutes.

Add water and salt to taste and simmer until potatoes are very tender, about 15 minutes.

Cook chorizo in a large nonstick skillet over moderately high heat, stirring occasionally, until browned, about 5 minutes.

Transfer to paper towels to drain.

Coarsely mash potatoes in pot with a potato masher (do not drain). Stir in chorizo and simmer 5 minutes. Stir in kale and simmer until just tender, 3 to 5 minutes. Season with salt.