Peel, quarter, core and cut the pears into small pieces. Sprinkle with lemon juice. Caramelise the sugar in a large pot until golden brown. Add pears and deglaze with pear nectar. Simmer covered for about 5 minutes.
Stir starch and about 4 tbsp. water until smooth. Stir into the compote, bring to the boil and simmer for about 1 minute. Let cool down for about 30 minutes. Then fold in frozen raspberries.
Mix vanilla sugar and cream stiffener. Whip cream until semi-stiff. Mix mascarpone until smooth, stir into the cream. Whip everything together for about 1 minute until stiff, while pouring in the vanilla sugar mixture. Pour cream into a piping bag with a large perforated spout.
Divide the compote into ten glasses (each containing approx. 125 ml). Spray mascarpone cream on top. Put it in a cold place. Just before serving, drizzle either crème de cassis or raspberry syrup over the cream.