Heat the oven to 150C/130C fan/gas 2. Using a dinner plate as a template, mark a roughly 25cm circle on a sheet of baking parchment in pencil, then flip the parchment over and put it on a large baking sheet or tray.
Whisk the egg whites with an electric whisk to stiff peaks, then whisk in the sugar, 1 tbsp at a time, until the meringue is glossy. Whisk in the vinegar, cornflour, ginger and vanilla. Dab a little meringue under all four corners of the parchment to help it stick to the baking tray, then spoon the meringue inside the marked-out circle using a palette knife or the back of a spoon. Spread the meringue to the edge of the circle, then create a dip in the middle – you want to create a ‘crater’, where the sides are higher than the centre, so the middle will hold the toppings.
Bake for 1 hr until the meringue is crisp and the base firm, then turn the oven off and leave the meringue to cool inside for 2 hrs.
Meanwhile, make the topping. Whisk the cream, sugar, stem ginger and ginger syrup together until the cream has just thickened and reached the soft peak stage.
To assemble, spread the ginger cream in the middle of the cooled pavlova, then sprinkle over the crushed biscuits and pomegranate seeds. Best eaten straightaway.