Cream the butter and sugar together until fluffy. Add eggs and egg yolks one by one while continuing to beat, then add salt, whiskey and vanilla. Stir in flour until a smooth dough is formed. Cover and refrigerate for 1 hour.
Roll out dough on a well floured surface until very thin, about 3mm thick. Cut dough into rectangles measuring 2x10 cm. Grasping each end of a dough strip, give it two twists to form a bowtie shape. Repeat with remaining dough.
Heat oil in a deep fryer to 190 degrees C.
Fry the biscuits in batches until golden brown on both sides, turning them over halfway through so they cook evenly. Drain on a paper towel-lined plate then dust with icing sugar.