Add the strawberries and rhubarb to a heavy bottomed saucepan.
Sprinkle over the sugar and cornflour and toss the berries and rhubarb until well coated in the sugar and cornflour mix.
Put the pan on a low-medium heat and cook gently until the fruit has softened and begun to let out their juices.
Continue to heat the fruit until the juices have mixed with the cornflour and begun to thicken.
Turn the fruit out into an ovenproof dish and let cool slightly while you make the crumble top.