- 1 lb dried cannellini beans (2 cups), picked over and rinsed
- 1 lb cipolline or small boiling onions (left unpeeled)
- 1 1/2 teaspoons salt (preferably sea salt), or to taste
- 2 lb large tomatoes, cored and halved crosswise
- 1 lb cherry tomatoes (preferably mixed colors; 4 cups)
- 1 teaspoon salt (preferably sea salt)
- 1 teaspoon sugar
- 1/2 cup extra-virgin olive oil
- 1/4 cup torn fresh basil leaves
- Cover beans with cold water by 2 inches in a bowl and soak at room temperature at least 8 hours or quick-soak (see cooks' note, below). Drain well in a colander.
- Blanch onions in boiling salted water , 1 minute, then drain and peel.
- Cover beans with cold water by about 1 inch in a 5- to 6-quart pot and bring to a boil. Add onions and simmer, partially covered, skimming froth as necessary, until beans and onions are tender, 40 minutes to 1 hour. Stir in salt and let stand (in cooking liquid), uncovered.
- Put oven rack in upper third of oven and preheat oven to 500°F.
- Toss tomato halves and cherry tomatoes with salt, sugar, and oil in a shallow 3-quart baking dish, then arrange tomato halves cut sides up. Roast tomatoes, uncovered, until large tomatoes are very tender with brown patches and cherry tomatoes are falling apart, 35 to 50 minutes.
- Transfer warm beans and onions with a slotted spoon to a deep large platter. Arrange tomatoes decoratively on top of beans and pour tomato juices on top. Sprinkle with basil leaves.