Preheat oven to 180°C.
Combine flour, baking powder and caster sugar in a bowl and whisk well.
Mix water and vanilla in a jug and set aside.
Whisk the egg whites with the stand mixer until soft peaks form.
In a separate bowl whisk the cream until fluffy,.
With a large spoon or spatula gently fold the egg whites into the cream until fully combined. Pour in the water and vanilla and stir lightly until just combined. Add the dry ingredients a little at a time, folding gently but thoroughly between each addition.
Spoon the mixture into cupcake cases until half full.
Bake for about 20 minutes but start checking at 15 minutes as each oven differs. The cupcakes are ready when a skewer inserted comes out clean.