1.Preheat oven to 120°C/250°F. Grease 3 oven trays; line with baking paper.
2.Whisk egg whites in a small bowl with an electric mixer until soft peaks form; gradually add caster sugar, 1 tablespoon at a time, beating until sugar dissolves between additions.
3.Gently fold in sifted cornflour and vinegar. Using 2 spoons; spoon 2 tablespoonfuls of meringue in mounds onto trays. Using the back of a spoon, create an indent in the centre of each mound for the filling.
4.Bake meringues for 40 minutes or until firm to the touch. Cool in oven with door ajar.
5.Meanwhile, combine strawberries, sifted icing sugar and 1 tablespoon of the sumac in a small bowl; cover, refrigerate for 3 hours.
6.Just before serving, whisk cream and vanilla in a small bowl with an electric mixer until firm peaks form. Spoon cream equally among meringues, top with sumac strawberries; sprinkle with remaining sumac to serve.
Don’t slice the strawberries too thinly or they will fall apart during refrigeration.Note