Mix the flour, salt, sugar, vanilla seeds and yeast in a bowl. Add the butter and milk, mix and knead into a soft, smooth dough. Cover and leave to rise at room temperature for approx. 1½ hrs. until doubled in size. Flatten the mixture a little, roll out to match the size of the tray, transfer to the prepared baking tray. Spread the jelly on top.
Arrange the pears on top of the dough. Mix the hazelnuts, flour, sugar, cinnamon and butter with a fork until the mixture is crumbly. Spread the crumble on top of the pears.
Approx. 45 mins. in the centre of an oven preheated to 180°C. Remove from the oven, leave to cool on a cooling rack. Cut the cake into pieces and dust with icing sugar.