Risotto with Black Beans

2 tbsp olive oil
1 large onion, finely chopped
salt and black pepper
2 small sweet potatoes (about 1 pound), peeled and cut into 1/4-inch pieces
2 cloves garlic, chopped
1 can black beans, rinsed and drained
1 cup Arborio rice
1 c. milk
1/2 cup grated Parmesan (2 ounces)
2 teaspoons chopped fresh oregano

Heat the oil in a large saucepan over medium heat. Add the onion, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Cook, stirring occasionally, until soft, 4 to 6 minutes. Add the sweet potatoes and garlic and cook, stirring occasionally, for 2 minutes.
Add the rice and cook, stirring, for 2 minutes. Add the beans and milk and cook, stirring frequently, until milk is absorbed.
Measure 3 1/2 cups of water. Add 3/4 cup at a time and cook, stirring occasionally and waiting until each addition is absorbed before adding the next. It should take 25 to 30 minutes for all the water to be absorbed.
Stir in the Parmesan and oregano.