Borlotti in Tomato Sauce

1 cup dried borlotti, pinto, or cranberry beans
2 tablespoons olive oil
1 medium red onion, halved and sliced
1 cup tomato puree

Soak beans overnight. Rinse and drain.

Heat oil in casserole. Add onion and cook about 3 minutes. Add beans, tomato puree, and 6 cups cold water. Raise heat to medium high and bring to boil. Reduce heat and simmer, partially covered, 2-3 hours, until sauce is thick. Salt to taste.
from Fagioli.