Preheat the oven to 140C/gas 1/
fan 120C. Line a large baking sheet
with non-stick parchment.
Blend the vinegar, vanilla and cornflour to a paste. Whisk the egg whites until stiff. Gradually whisk in the sugars, adding a little paste with each addition, until a thick marshmallowy meringue is formed.
Spread it out to a 20cm circle on the baking sheet, swirling the knife to make peaks. Scatter over the nuts and bake for 1 hour, then turn off the oven and leave it to cool.
Sieve 100g/4oz strawberries into a bowl. Stir in the cassis. Whip the cream softly. Slice half the strawberries and fold into the cream. Then swirl in 3 tbsp sauce.
Put the pavlova on a flat plate. Spoon in the cream, scatter on the strawberries, drizzle with sauce.