Boil the sugar and water in a wide stainless steel pan without stirring. Reduce the heat and simmer, swirling the pan occasionally until a light brown caramel has formed. Remove the pan from the heat. Mix in the nuts, pour in the cream, return the pan to the hob, reduce the liquid slightly over a low heat. Transfer the nuts to a bowl, leave to cool.
Shortcrust pastry crumble
Mix the flour, salt, sugar and lemon zest in a bowl. Add the butter, rub by hand to form a crumbly mixture, spread onto a baking tray lined with baking paper.
Bake for approx. 20 mins. in the centre of an oven preheated to 180°C. Remove, leave to cool.
Combine the quark with the whipped cream, vanilla sugar and sugar. Layer the quark cream, nuts and shortcrust pastry crumble in bowls or glasses, top with the crumble.