Place beans in large bowl and add water to cover by 2 inches. Let stand overnight. Drain and rinse beans before using. In large soup pot, melt butter over medium-high heat. Add leeks and cook, stirring occasionally, until softened, about 2 minutes. Stir in cabbage and continue cooking until cabbage is wilted. This will be about 8 minutes. Add beans, bay leaf, and vegetable stock. Reduce heat to low and simmer until beans are tender, about 1 hour. Stir in cream, parsley, tarragon, salt and pepper, simmer to heat through, 5 minutes longer, and serve. Serves 8.