Preheat the oven to 180C/360F/Gas 4.
Whisk the egg whites in a bowl until stiff peaks form when the whisk is removed.
Add the sugar, one tablespoon at a time, whisking constantly, until all the sugar is combined and stiff peaks form when the whisk is removed.
Gently fold in the vinegar, pink food colouring and orange liqueur.
Divide the meringue mixture into two equal portions. Spread the meringue mixture onto two baking trays lined with baking parchment.
Transfer to the oven and turn the oven temperature down to 150C/300F/Gas 2.
Bake the meringue for about one hour. The result should be crisp on the outside and chewy in the middle.
For the filling, whisk the cream with the vanilla seeds and sugar until stiff peaks are formed when the whisk is removed. (You can use the vanilla pod in another dish.)
Spoon equal amounts of the cream mixture onto both of the cooked meringues.
Place equal amounts of the strawberries on top of the two cream-covered meringues.
For the sauce, place the sugar and water into a pan over a medium heat and bring to the boil. Boil for 12-15 minutes, until the liquid becomes a thick syrup.
Remove from the heat then add the strawberries and set aside for ten minutes. Transfer the strawberries and syrup to a food processor and blend until smooth, then pass through a sieve. Place into the fridge to chill.
To serve, cut each pavlova in half and place each half onto a plate. Pour over the strawberry sauce and serve.