Preheat the oven to 180ºC. Grease and line the base of a 20x30cm baking tray. Sift the flour and baking powder into a large bowl and then rub in the butter with your fingertips.
Stir in both the sugars. Press half the mixture over the base of the tin. Lay the peaches over the top and sprinkle with raspberries.
Add the vanilla extract, extra baking powder, egg and milk to the rest of the base mixture and stir well – don’t worry too much about lumps. Pour evenly over the top of the peaches and raspberries and bake for 1 hour.
Cool in the tray and then cut into squares to serve.
