2) Immerse the peaches in boiling water for 30 seconds, then place them in cold water. Peel off the skins and slice the peaches into thick wedges.
3) Place the peach wedges into a large bowl and add the orange zest, 55g of the granulated sugar, 100g of the demerara sugar and 2 tbsp of the flour. Toss well.
4) Gently mix in the raspberries. Allow the mixture to sit for 5 minutes. If there is a lot of liquid, add another tablespoon of flour. Pour the peaches into the baking dish and gently smooth the top.
For the topping:
1) Combine the 210g of flour, the remaining granulated and demerara sugar, salt, oatmeal and the cold, diced butter in the bowl of an electric mixer fitted with a paddle attachment.
2) Mix on a low speed until the butter is pea-sized and the mixture is crumbly. Sprinkle the crumble evenly on top of the peaches and raspberries.
3) Bake for 1 hour, until the top is browned and crisp and the juices are bubbly. Serve immediately, or store in the refrigerator and reheat in a preheated 180C/Gas mark 4 oven for 20 to 30 minutes, until warm.