Preheat your oven to 375°F (190°C). Grease a baking dish or individual ramekins with butter or cooking spray.
In a large mixing bowl, combine the gooseberries, blackcurrants and granulated sugar. Toss until the fruit is evenly coated, then transfer the mixture into the prepared baking dish or ramekins.
In another mixing bowl, prepare the crumble topping. Combine the all-purpose flour, rolled oats, brown sugar, cold diced butter (113 grams), ground cinnamon, and a pinch of salt. Use your fingertips or a pastry cutter to rub the butter into the dry ingredients until the mixture resembles coarse breadcrumbs.
Sprinkle the crumble topping evenly over the fruit mixture in the baking dish or ramekins.
Place the baking dish or ramekins on a baking sheet to catch any drips, then transfer to the preheated oven.
Bake for 30-35 minutes, or until the fruit is bubbling and the crumble topping is golden brown and crispy.
Remove from the oven and allow to cool slightly before serving.
Serve warm, optionally with a scoop of vanilla ice cream or a dollop of whipped cream.