Heat oven to 180C/160C fan/gas 4. Dust your work surface with a little gluten free flour, then roll out the pastry into a circle roughly 35cm in diameter. line a large baking sheet with parchment and lay the pastry on top.
Put the strawberries in a bowl and toss through the cornflour and sugar. Sprinkle the pastry with 1 tbsp sugar, then arrange the strawberries on top, leaving a border about 3cm clear around the edge.
Beat the remaining egg and sweep over the pastry edge with a brush. Fold the pastry over the strawberries, pinching to create a rough border, and leaving the centre exposed.
Brush the edge with more egg. Bake for 45-50 mins until golden brown and crisp. Brush the strawberries with the jam. leave to cool for 15 mins before serving with lactose free cream, if you like.