2) Mix together the cornflour slurry and lemon juice and stir into the peaches to incorporate. Butter a 30cm by 20cm oval dish and add the peach mixture.
3) For the topping; in a medium bowl, combine the dry ingredients, add in the butter pieces and combine with the hands until crumbly.
4) Top the peaches with half the crumble topping. Place in the oven and immediately reduce the temperature to 180C/Gas 4. Bake uncovered for 30 mins, then add the remainder of the crumble topping.
5) Reduce the heat to 160C/Gas 2 and bake until golden and bubbling, another 45 mins. Remove from the oven and leave to sit for 15 mins before serving.
6) Serve with vanilla ice cream or fresh whipped cream.