Preheat oven to hot. Cover a greased flat baking tray with gladbake (??) or a split open oven bag. Grease well with butter, sprinkle with cornflour and tap off excess (the cornflour gives a nice dry surface under the pavlova.

Using a 18 cm (7 inch) cake tin as a guide, mark out a circle on the tray with a skewer.

Beat egg whites and salt until stiff. Add sugar 1 heaped tablespoon at a time until all sugar has been added. When finished, the meringue should be thick and shiny. Stir in vinegar, cornflour and vanilla, stir gently then pile onto prepared tray. The mixture should stay roughly in the marked circle, simply smooth over the top (It is important not to make the mistake of scooping out the centre). The mixture should be about 2-1/2 inches high for a good marshmallow centre. Drop oven temperature to very slow before placing the pavlova in the oven. Bake for 1 1/4 hours. Remove from oven and cool for a few minutes, then turn upside down onto a flat serving plate. Remove paper or ovenwrap carefully. The centre will sink slightly as the pavlova cools. When cold, fill with whipped cream and top with sliced bananas, passion fruit pulp and whole strawberries (but don't fill until right before you serve).