Cut the fennel bulbs into quarters and blanch them in boiling water for 5 minutes. Drain well.
Melt the butter in a frying pan over medium heat, add the fennel and fry until browned, then add the brown sugar and caramelise. Add the vinegar and stock, then cover and simmer until the bulbs are tender. Remove the lid and boil until the liquid is reduced, then stir in the cream