Line a box form (approx. 1.5 l capacity) with baking paper. Finely chop Toblerone for the ice cream mixture. Cut the vanilla pod lengthwise and scrape out the pulp with a knife. Separate the eggs.
Beat the egg whites and cream separately until stiff and cover and chill. Whip vanilla pulp, egg yolk and 100 g sugar with whisk of mixer for 3-5 minutes until white-creamy. First fold in Toblerone, then cream, then beaten egg whites.
Smooth the mixture in the mould. Cover with foil, freeze for at least 5 hours.
Wash, stalk and stone the cherries. Boil up cherry nectar with 5 tablespoons of sugar. Stir starch with 2-3 tablespoons of water until smooth and bind the nectar with it. Add cherries and simmer for 2-3 minutes.
Allow Semifreddo to thaw in the mould at room temperature for 10-15 minutes. Cut into slices, possibly refreeze the rest. Serve the semifreddo and hot cherries. Keep any remaining cherries cold in screw-top jars.