Preheat the oven to 140C, fan 130C. In a large, clean bowl, whisk the egg whites and cream of tartar to soft peaks, then slowly whisk in the caster sugar, a quarter at a time, until the mixture is thick and glossy.
Spoon a third of the egg mixture into a separate bowl and beat in the Rosewater, 2 tbsps of the pistachios and the food colouring, if using.
Using a metal spoon, carefully fold this back into the rest of the egg mixture, then sift in the icing sugar and gently fold this in too.
Spoon two tablespoons of the meringue mixture onto the baking trays and sprinkle the tops with the remaining pistachios. Place these in the oven, then lower the oven temperature to 120C, fan 110C. Bake for 45 minutes, then leave in the oven to cool completely before removing. (overnight is ideal)
To make the vanilla cream, whisk the double cream with the vanilla seeds until it forms soft peaks. Serve the meringues with the strawberries and vanilla cream.