Preheat the oven to 325F. Line a baking sheet with baking parchment and draw a 12in circle on the paper. Draw a 6in circle in the center of the 12in circle.
Put six egg whites into a mixing bowl and whisk with an electric whisk until they look like clouds. Gradually add the sugar a little at a time, whisking on maximum speed until they are stiff and glossy. Mix the lemon juice and corn starch in a cup until smooth, then stir into the bowl.
Spoon the meringue between the 2 circles on the baking parchment, to make a wreath shape. Using a large spoon make a trench in the meringue for the cream and fruit to sit in. Slide into the oven, then immediately reduce the temperature to 300F and bake for 1 hour – 1 hour 15 minutes. Turn the oven off and leave the pavlova inside for an hour or overnight to dry.
Add the whipped cream and fruit right before serving as the moisture from both as well as weight will begin to break down the Pavlova.
To assemble, whip the cream and powdered sugar until just stiff.
Spoon half of the cream into the trench in the meringue. Arrange 1/3 to ½ of the fruit on the whipped cream. Then put on the rest of the whipped cream and the rest of the fruit.
To serve, dust with powdered sugar and cut in wedges.
The pavlova can be made up to 1 month ahead and stored: wrap it in cling film and then foil and keep in a cool place.