Cut the butter into pieces, place each potato on a piece of foil with the rosemary and a knob of butter. Season the potatoes, seal the foil at the top and place on a baking tray.
Bake for approx. 50 mins. in the centre of an oven preheated to 200°C.
Tomato & cheese fondue
Heat the oil in a fondue pot, press the garlic and add to the pot with the tomato puree, cook briefly. Pour in the tomato juice and bring to the boil. Grate the cheese directly into the fondue pot. Stir the cornflour into the water, add to the pot while stirring. Bring the fondue to the boil, stirring constantly, reduce the heat, continue to simmer until the cheese has melted.
Add the thyme and sugar, season the fondue.