Make the pavlova the day before and then whip the cream and prepare the fruit at the last minute.
Heat the oven to 180C/fan 160C/gas 4. Cover a baking sheet with baking parchment. Whisk the egg whites with electric beaters until they just form stiff and
shiny peaks. Gradually add the sugar a couple of tablespoons at a time and whisk really well between each addition. When all of the sugar is used up continue whisking for 3–4 minutes or until the meringue is stiff and glossy and stands up in peaks, then whisk in the cornflour and vinegar. Spoon the mixture onto the baking parchment and use a palette knife to make a circle about 20cm in diameter. Put in the oven, turn the temperature down to 120C/fan 100C/gas ½ and cook for 1½ hours. Turn the oven off and leave the meringue inside until completely cold (you can make this the day before and leave to cool overnight).
Carefully peel off the baking parchment and put the pavlova on a serving dish. Don’t worry if it cracks.
Scrape the vanilla seeds into a mixing bowl, add the cream and lemon zest and softly whip, then spoon onto the pavlova. Mix the berries, spoon the fruit on top of the cream, dust with a little icing sugar and serve.