Preheat the oven to 160°C fan (320°F) or 170°C conventional (340°F).
Cut the peaches into chunky wedges and place them in a large bowl.
Add the fresh raspberries and 75 g caster sugar. Gently toss until the fruit is evenly coated without crushing the raspberries.
Transfer the fruit mixture to an ovenproof baking dish and spread it into an even layer.
In a separate large bowl, combine the plain flour, baking powder, caster sugar, and lemon zest.
Add the cold butter. Rub it into the dry ingredients with your fingertips until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining.
Add 2 teaspoons of milk and gently mix until a soft, cookie dough-like topping forms. If the mixture remains very dry and crumbly, add a small amount of additional milk.
Spoon pieces of the topping evenly over the fruit. You do not need to completely cover the peaches and raspberries; small gaps allow the colorful fruit juices to bubble through.
Sprinkle the flaked almonds over the topping. Add a light sprinkling of demerara sugar if desired.
Bake the Easy Peach and Raspberry Cobbler for 25–30 minutes, or until the fruit is bubbling around the edges and the topping is cooked through and golden.
Remove from the oven and allow the cobbler to rest for about 10–15 minutes before serving.