Beat together egg whites, salt and cream of tartar to soft peaks in a large bowl. Beat in sugar about three tablespoons at a time, until stiff and glossy peaks form. Sift cocoa and cornflour over egg whites and gently fold in. Gently fold in vinegar, vanilla and 60g melted chocolate.
Line a baking tray with baking paper and spread the meringue into a 20cm circle. Bake in the centre of the oven for 1 1/2 hours until the outside is crispy and the centre is soft. Using a metal spatula, loosen the meringue from the baking paper and remove to cool on a wire rack. Allow to cool completely, about one hour.
Whip cream with 2 teaspoons sugar and spread over the meringue. Arrange strawberries decoratively over the top and drizzle with melted chocolate.