• 1 litre milk (not skimmed, sterilised or anythinged, ordinary milk!)
• 8 egg yolks
• 230 g caster sugar
• a few drops of vanilla essence
• 500 ml double cream

Scald the milk, i.e. heat it until nearly boiling. Whisk the egg yolks with 80 g of the sugar by hand in a heavy saucepan until just combined, then pour in the hot milk, whisking all the while. Heat to 80°C/176°F, or until it thickens enough to coat the back of a metal spoon. Add the vanilla essence, and allow to cool, stirring.

Use a stainless-steel, aluminium or pale enamelled wide pan: the reason for this is that it will allow you to judge the degree of brownness in the melting sugar. Dark pans hide the colour, and the tendency would be to undercook the sugar, resulting in toffee, not caramel. Melt the remaining 150 g sugar over a medium heat. Do not stir, swirl the pan instead (if you stir, half the sugar will cling to the spoon). Take the sugar to dark brown (not tan, not café au lait but dark brown). Remove from the heat and rather gingerly pour in the double cream. It will splutter and spit for a few seconds. Stir and return to a low heat until all the lumps of caramel that formed on contact with the cold cream dissolve into it. You have just made a butterscotch sauce.

Combine the ice cream mixture and the caramel cream mixture, then freeze in the same manner as the Vanilla Ice Cream.