01 - Set the oven to 350°F (180°C) to preheat.
02 - In a large bowl, combine plums with sugar, cornstarch, cinnamon, ginger, nutmeg, and lemon juice; toss until evenly coated.
03 - Spread the plum mixture evenly in a 9-inch (23 cm) baking dish.
04 - In a separate bowl, mix flour, oats, brown sugar, and salt. Add cold butter cubes and rub in with fingertips until the mixture resembles coarse crumbs.
05 - Evenly distribute the crumble topping over the plums.
06 - Bake for 35 to 40 minutes until the topping is golden and the fruit is bubbling at the edges.
07 - Let the dish cool slightly before serving warm; optionally serve with vanilla ice cream or custard.