In a large bowl, pour beans, add water to a level of 3 inches above beans and soak for 6 hours or overnight. Drain. Place beans in a soup kettle or Dutch oven; add 7 cups of water, 5 sage leaves and tomato. Bring to a boil; reduce heat and simmer uncovered for 1-1/2 to 2 hours or until beans are almost tender. Drain and reserve beans; discard liquid, sage and tomato. In a large saucepan, heat oil over medium heat. Add garlic, remaining sage, onions, carrots, celery, red pepper flakes and sauté until tender. Add beans, crushed tomatoes, stock, salt and pepper. Cover, reduce heat to low, continue to cook for 15-20 minutes.
Meanwhile in a large skillet, prepare sausages according to package directions. Drain. Cut sausage links into thirds. Just before serving, gently stir mascarpone cheese into beans. Spoon prepared beans into individual bowls and top with sausage pieces. Garnish with additional fresh sage. Serve.
*1/3 cup cream cheese, cubed, may be substituted for mascarpone cheese.