2) Whisk together the buttermilk, egg, egg yolk and vanilla in a small bowl and then add to the flour mixture and beat until smooth. Beat in the remaining flour until combined. Cover and refrigerate for at least 1 hour and up to 6 hours.
3) Turn the dough out onto a floured surface and roll out to 1cm thick. Using a 7.5cm round biscuit cutter, cut the dough into rounds. Using a 2cm biscuit cutter, cut a hole from the centre of each round. Gather the scraps and re-roll the dough, cutting additional doughnuts until the dough is used up.
4) Heat 13cm of oil in a large pan to 180C. Add the doughnuts, three at a time, and fry until golden on both sides, turning once, about 4 to 5 minutes in total. Transfer to a plate lined with paper towels.
5) When doughnuts have cooled, dip the tops in the bourbon-praline mixture and place on baking racks until the praline sets slightly. Sprinkle nuts on top.
For the bourbon praline:
1) Combine the sugar, water, vanilla pod and seeds in a medium saucepan over high heat and cook to a dark amber colour.
2) Remove the mixture from the heat and slowly whisk in the cream, butter and salt. Return to the heat and whisk until smooth.
3) Remove from the heat and whisk in the bourbon. Strain. Leave to cool until slightly thickened.