Heat the oil in a frying pan and brown the sausages on all sides. Remove from the pan and reserve. Add the shallots, carrots and celery to the pan and sauté for 5 minutes, then add the garlic, rosemary and bay leaf and cook for a further minute.
Add the wine and stock, bring to the boil, then add the flageolet beans, tomatoes and redcurrant jelly. Return the sausages to the pan and simmer for 30 – 40 minutes, until the sauce has thickened and the beans are soft and cooked through. Add the olives and cook for a further five minutes. Check the seasoning, remembering the olives are salty, and adjust as necessary.
For the crostini, mix together the crushed garlic and softened butter, and season with sea salt and black pepper. Spread the garlic butter onto both sides of the baguette slices, and grill each side until golden.
Sprinkle the parsley over the cassoulet and serve with the garlic crostini.