No need to preheat the oven just yet, the pastry needs to chill. Place the flour, sugar, salt and butter into your food processor and blitz until you have a breadcrumb texture. Slowly add the water, 1tbsp at a time, pulsing in between additions, until the pasty balls up into one large lump. Don't be tempted to add more water. It really only needs up to 4tbsp. It will go through a phase of looking like it won't come together, but keep blitzing and it will.
Alternatively, place the flour, sugar, salt and butter into a large bowl and either use a pastry cutter or your fingers to cut the butter into the flour. Keep going until you have a coarse bread crumb texture, then slowly add the water and mix into one lump of dough.
Tip the pastry onto a sheet of cling film and flatten into a disc. Wrap and place in the fridge for 30 minutes.
Once the pastry has chilled, preheat the oven to 200C/400F and line a baking tray with grease proof paper.
Place the strawberries, peaches, vanilla and sugar into a medium sized bowl and stir to coat everything with the sugar. Leave to one side while you roll out the pastry.
Flour your worktop or use a lightly floured silicone pastry mat. Unwrap the pastry and place onto your surface. Roll the pastry out into a 10-12 inch round, it doesn't have to be perfect, the beauty of galettes is that they look rustic!
Transfer the pastry onto your lined baking tray - I lightly flour my rolling pin and then take the top edge of the pastry, place it over the rolling pin and continue to gently bring the rolling pin towards me looping the pastry loosely around. Lift and transfer, then unroll the pastry.
Spoon your fruit into the centre of your pastry and spread into an even layer, Leave a border of about 2-3 inches all the way round.
Take a 2-3 inch length of the border and fold it up over the fruit. Then move along to another 2-3 inch length and fold that over, overlapping the previous one to give you a pretty fold. Continue until you have gone all the way around and folded all the pastry. Sprinkle the edges with demerara sugar and place in the oven for 30-35 minutes, until the pastry is golden and the fruit is bubbling.
Leave to cool on the tray for 30-45 minutes or completely. You can serve this galette warm or at room temperature. If you want to glaze your fruit to make it glossy, place 1tbsp of apricot or strawberry jam into a small heat proof bowl and microwave for 20-30 seconds, just until it's easy to brush. Brush the jam all over the fruit and then serve with ice cream.
Strawberry Peach Galette will keep in an airtight container, in the fridge for 4 days.