Preheat the oven to 130°C/250°F/Gas mark 1⁄2.
Mix together the egg whites, sugar and vinegar in a clean grease-free heatproof bowl, and put over a pan of gently simmering water. Beat with an electric whisk for 10 minutes or until very stiff and shiny.
Line a baking sheet with non-stick baking parchment, and spread the meringue mixture into a rectangle using a metal spatula or palette knife. Bake for 40 minutes, turn off the oven and leave the meringue inside to cool completely.
Whip the cream until it just holds its shape, and spread over the cold pavlova. Sprinkle with the nuts, and chill for 2–3 hours or overnight. Cut into thick slices to serve.