1 medium leek, white and tender green parts only, sliced crosswise 1/4 inch
1 large garlic clove, minced
1 poblano chile, cut into 1/2-inch dice
2 large plum tomatoes-peeled, seeded and cut into 1/2-inch dice
1 teaspoon chopped thyme
1 teaspoon chopped tarragon
Salt and freshly ground pepper
In a medium saucepan, cover the cranberry beans with 1 inch of water. Add the bacon and onion and bring to a boil. Simmer over low heat until the beans are tender, about 15 minutes. Discard the bacon and onion and transfer the beans and their cooking liquid to a bowl.
In the same saucepan, heat the olive oil. Add the leek, garlic and poblano and cook over low heat, stirring occasionally, until softened, about 12 minutes. Add the beans and their cooking liquid and bring to a simmer. Add the tomato and simmer over moderate heat until tender, about 3 minutes. Stir in the thyme and tarragon and season with salt and pepper. Serve the stew hot or warm.
The stew can be refrigerated for up to 2 days. Reheat gently before serving.