Heat oven to 150C/130C fan/gas 2. Using a pencil, mark out the outline of a dinner plate on baking parchment. Whisk the egg whites with a hand mixer until they form stiff peaks, then whisk in the sugar, 1 tbsp at a time, until the meringue looks glossy. Whisk in the vinegar, cornflour and vanilla.
Spread the meringue inside the circle, creating a crater by making the sides a little higher than the middle. Bake for 1 hr, then turn off the heat and let the Pavlova cool completely inside the oven.
When the meringue is cool, chop 100g of the strawberries and mix them with 2 tbsp icing sugar. Place in a food processor, blitz until smooth, then push the fruit mixture through a sieve. Whip the Lactofree cream with the remaining icing sugar and spread it over the meringue. Put the remaining fruit on the cream and finally pour the sauce over the lot!