1.Combine fruit and 1 cup of the whiskey in large bowl. Cover with plastic wrap; stand overnight.
2.Preheat oven to 120°C/250°F. Grease deep 20cm (8-inch) round cake pan; line with two layers of baking paper, extending paper 5cm (2 inches) over edge of pan.
3.Stir remaining whiskey and ½ cup of the sugar in small saucepan over heat until sugar dissolves; bring to the boil. Cool syrup 20 minutes.
4.Meanwhile, beat butter and remaining sugar in small bowl with electric mixer until just combined (do not overbeat). Beat in eggs, one at a time. Add butter mixture to fruit mixture; stir in ground hazelnuts, sifted dry ingredients and ½ cup of the cooled syrup. Spread mixture into pan.
5.Bake cake 3½ hours. Brush cake with reheated remaining syrup, cover cake with foil; cool in pan.