Cut out the stalk, carefully remove the leaves and cut the thick leaf ribs flat. Blanche the leaves, in batches, in salted water for approx. 5 mins. then briefly rinse in cold water. Arrange 8 large leaves on a cloth and place smaller leaves on top.
Brown the meat in the oil. Add the onion and sage and cook briefly. Sprinkle the flour over, mix, pour in the stock, season, simmer for 5-10 mins., leave to cool. Mix in the meat and diced potato.
Fill the rolls and braise
Distribute the filling evenly over the leaves, fold the edges of the leaves inwards, tie the rolls up with kitchen twine then transfer, seal facing downwards, to a greased, ovenproof dish, pour in the stock and seal the dish with foil.
Braise for approx. 40 mins. in the centre of an oven preheated to 200°C. Remove the foil after 20 mins.
Remove the rolls from the oven and keep warm. Strain the liquid back into a small pan and reduce to approx. 100 ml. Stir in the single cream and tomato puree, simmer for approx. 2 mins., season the sauce.