Place a large heavy saucepan over a medium heat and add the butter

When the butter has melted, add the sugar and stir frequently until the mixture is a deep golden brown caramel

Remove from the heat and immediately whisk in half of the double cream (the mixture will bubble up furiously and may splatter so be sure to wear an oven mitt)

Stir in the rest of the cream, vanilla extract and salt and mix until the caramel is smooth. Set aside to cool slightly

When you are ready to serve the sundaes, place 2 sharing-sized sundae glasses, the ice cream tubs, salted caramel sauce and butterscotch popcorn on the worktop in front of you

Pour a little salted caramel sauce in the bottom of each sundae glass and add a few pieces of popcorn, followed by a scoop of each flavour of ice cream

Repeat in layers until you reach the top of the glasses. Add a final sprinkle of popcorn, wafers, and a drizzle of sauce and serve immediately