01 -
Heat the oven to 190°C / 375°F. Pit the plums and cut into thick wedges. Place in a 1.5-liter baking dish.
02 -
Toss plums with 40 g of the brown sugar, cornstarch and half the cinnamon. Spread into an even layer.
03 -
Mix flour, oats, salt, remaining 60 g brown sugar and remaining cinnamon in a bowl. Cut the cold butter into cubes.
04 -
Rub butter into the dry mixture with fingertips until there are both fine crumbs and pea-sized clumps. Scatter over the fruit without pressing down.
05 -
Bake for 35–40 minutes until the topping is golden and fruit juices bubble visibly around the edges. Place the dish on a tray to catch drips.
06 -
Rest 15 minutes so the juices thicken slightly. Serve in bowls, spooning both fruit and crumble into each portion. The filling should remain juicy rather than slice like a pie.
07 -
Cool and refrigerate covered within two hours for up to four days. Reheat portions until hot throughout; an oven preserves more crunch than a microwave.