Preheat oven to 180℃.
Peel your apples, then chop them into smaller pieces.
Add the chopped apple to a pan on medium heat, with a splash of water. Leave to simmer and soften.
Whilst the apples are stewing, make the crumble topping. In a large bowl mix the flour, oats, walnuts, and the 1/2 cup of brown sugar.
Add the cubed butter to the flour mix. Use your hands to mush it all together, try to leave some of the butter in small chunks. You will want a moist crumbly texture, set the mix aside.
By now the apples should have started softening. Add drained peaches to the pan, cook off any leftover juice.
To the fruit in the pan, dd your desired amount of cinnamon, a pinch of salt, and the remaining 1/4 cup of brown sugar.
Turn the heat up slightly, allow the peach and apple mix simmer. Leave to caramelise.
Grease an oven safe dish, and pour the fruit mix in.
Add the crumble topping, breaking it into smaller pieces as you layer it.
Place in the oven for 25-30 minutes, until the crumble is golden in colour.