Preheat oven to 180ºC. Allow pastry to defrost, before cutting it into a circle shape. Circle should be approximately 20-25cm in diameter.
In a bowl, combine blueberries, Natvia, cornflour and lemon juice. Allow to sit for 10 minutes to give the blueberries time to defrost. Stir to ensure that the liquids mix with the cornflour, creating a coating over the fruit.
Pour into the centre of your pastry circle and roughly fold in the edges.
Using a pastry brush, brush cream or milk over the pastry to give it a shine when it is baked.
Bake galette for 35 minutes until the pastry is golden. Allow to cool for 10 minutes before serving with frozen yoghurt, ice cream or cream.