Dissolve the sugar and golden syrup in a pan over low heat.
Cook the mixture on high heat until it turns into a golden-brown caramel.
Stir in the bicarbonate of soda and pour onto a lined baking tray to cool.
Whip the double cream until it is thick but not fully stiff.
Fold in the vodka and condensed milk, then whisk until stiff peaks form.
Break the cooled honeycomb into pieces and fold them into the cream.
Place the mixture in a container and freeze for at least eight hours.
Preheat the oven to 180°C.
Beat the butter and sugar together until light and fluffy.
Mix in the flour and processed pistachios until combined.
Press the mixture onto a lined baking sheet and score 5cm x 7cm rectangles.
Bake for 8 to 10 minutes until golden, then cool on a wire rack.
Serve two scoops of ice cream with two pieces of shortbread.