Use a sharp knife to cut a pocket in the side of the meat.
Prepare 4 small skewers to seal the opening after the filling is added.
Wash the fennel, remove the leafy tops and quarter lengthways.
Peel and very finely dice the carrot, celery, onion and garlic. Cut the tuna into 2cm cubes.
Heat 1 tbsp oil in a pan. Add the vegetables and fry for 3 minutes over a medium heat until softened. Add the tuna and seal on all sides. Add 4 tbsp cream and simmer for 2-3 minutes. Season with salt and pepper. Leave to cool, then chop to a paste in a blender.
Spoon the tuna mixture into the pocket and close with the skewers. Heat 2 tbsp oil in a pan and fry the meat for 3-5 minutes until browned on both sides. Place on a plate and keep warm in a low oven. Pour in the wine and the rest of the cream, bring to the boil and reduce to a creamy sauce. Season with salt and pepper.
Heat the remaining oil in a pan and fry the fennel for 8 minutes, turning regularly until tender but still slightly crisp. Season with salt and pepper.
Serve the meat with the fennel and drizzle with the sauce. Garnish with fennel leaves and serve with baguette.