2 tablespoons extra-virgin olive oil
2 oz thinly sliced Black Forest ham, chopped (1/2 cup)
1 1/2 cups thinly sliced scallions (from 1 bunch)
1 tablespoon chopped garlic (2 cloves)
1 Turkish or 1/2 California bay leaf
2 lb green unripe tomatoes, chopped
1 cup low-sodium chicken broth
2 cups water
1/2 teaspoon salt
1/4 teaspoon black pepper
Garnish: sour cream (optional)
Heat oil in a 3-quart heavy saucepan over moderate heat until hot but not smoking, then cook ham, stirring occasionally, until beginning to brown, 1 to 2 minutes. Add scallions, garlic, and bay leaf and cook, stirring occasionally, until scallions are tender and lightly browned, 6 to 8 minutes.
Add tomatoes, broth, water, salt, and pepper and simmer, partially covered, until tomatoes are tender, 15 to 20 minutes. Discard bay leaf and season soup with salt and pepper.