Pre-heat the oven to 160C(320F) fan-forced and line a tray with baking paper. Trace around a plate onto the baking paper to make an outline for the meringue base.

Beat the egg whites in the bowl of an electric mixer until soft peaks form. Add the caster sugar in 6 batches, beating for 20 seconds between additions.

Continue to beat until the mixture is thick and glossy.

Add the cocoa, vinegar and cream of tartar and whisk just until they are mixed in.

Take the bowl off the mixer and gently fold through the chopped chocolate.

Scrape the meringue out of the bowl onto the circle on the baking paper. It will expand so leave at least a one centimeter space between the meringue and the border. Smooth out the top and sides.

Put the pavlova in the oven and turn it down to 130C(266F) fan-forced. Bake it for 1 hour or until it has cracked and is hard on the outside.

Turn off the oven and open the oven very slightly. Leave it to cool completely in the oven. It will take at least 3 hours.

Make the butterscotch sauce but combining all the ingredients in a small saucepan. Heat the mixture, stirring, until everything has dissolved and then bring it to a boil.

Reduce to a simmer and cook, stirring until it thickens. It will take at least 15 minutes.

Transfer the sauce to a jug and leave it to cool.

To serve, pile the pavlova with whipped cream, swirl through the butterscotch sauce and sprinkle it with the grated chocolate and salt flakes.

Serve immediately.