Preheat your oven to 180°C (160°C Fan)
Gas mark 4. Lightly grease a 23cm x 23cm (9×9-inch) square baking dish.
Prepare the fruit filling: Rinse the nectarines, cut them in half, remove the stones, and slice into 1cm thick wedges. Place the nectarine slices into a large mixing bowl.
Add the granulated sugar, cornflour, lemon juice and vanilla extract to the nectarines. Gently mix until the nectarine slices are coated evenly. Transfer the fruit mixture to the prepared baking dish and spread it out evenly.
Prepare the crumble topping: In a medium mixing bowl, combine the plain flour
(and ground almonds if using), cubed butter, granulated sugar, rolled oats and salt. Use your fingertips or a pastry blender to work the butter into the dry ingredients until the mixture resembles coarse crumbs.
Sprinkle the crumble topping evenly over the nectarines in the baking dish, ensuring that the fruit is fully covered. Add some flaked almonds for texture.
Bake the nectarine crumble in the preheated oven for 35-40 minutes, or until the topping is golden brown and the fruit is bubbling.
Remove the crumble from the oven and let it cool slightly for 10-15 minutes before serving. Enjoy the nectarine crumble warm, preferably with a scoop of vanilla ice cream or a dollop of crème fraiche.
Note: If nectarines are not available, you can substitute with an equal weight of
peaches or plums