Preheat your oven on 170c fan/190c/375F/Gas mark 5.
In a lidded pan, gently melt the butter and add the quartered plums, sugar and lemon juice with zest giving it a good stir. Then over medium heat, cook for 2 minutes without the lid following with 2 minutes with the lid.
Pour the plums in to the deep square dish and now to make the crumble.
In a large mixing bowl, mix together the flour and baking powder then rub in the cubed butter until you get crumbs.
Stir in the sugar with a fork and finally, mix in the cookie crumbs and sprinkle over the plums, ensuring everything is covered.
Place the baking dish on to a tray and bake for 30 minutes and serve with ice cream or custard.