Start this recipe by making the thyme strawberry jam. Place the frozen strawberries, lemon zest, 50g caster sugar and thyme sprigs into a pan and cook down for 10 minutes to form a jam. Cool down completely. When ready, unroll the 2 sheets of puff pastry and cut into 2 x 8inch rounds. Brush the edges with a little water and spread over the jam, leaving a gap of 1inch empty all the way around. Place a layer of the sponge over the jam then cover with the cold custard. Decoratively lay over the sliced strawberries and fold in the extra pastry, pleating to create a galette. Brush the 2 galettes with a little water, sprinkle over the 2 tbsp. caster sugar and place onto baking sheets. Bake in the oven at 200°C for 25-30 minutes or until golden brown. Serve chilled with the strawberry ice-cream on the side.