Preheat the oven to 140oC, gas mark 1. Draw a 23cm circle onto a sheet of baking paper and place on a large baking tray.
Blend the cornflour with the vinegar and vanilla. Whisk the egg whites to stiff peaks and gradually whisk in the sugar a tablespoon at a time. Whisk in the cornflour mixture and continue to whisk for 2-3 minutes until stiff and glossy. Chop 75g of the walnuts and stir all but 1 tbsp of this into the meringue. Spoon onto the paper up to the line with a slight hollow in the centre. Sprinkle with the remaining 1 tbsp chopped walnuts and bake for 1 hour. Turn the oven off and leave the pavlova inside until cooled.
Whisk the cream to soft peaks and spoon over the pavlova leaving a 3cm border round the edges, top with the strawberries and remaining walnuts.
Cooks tip
Try making 6-8 individual pavlovas instead of a large one and top with other summer fruits.