Preheat the oven to 450°. Toss together the cauliflower, onion, apple, olive oil, and salt in a large shallow baking dish and spread the ingredients out into a single layer. Bake for 20–30 minutes, stirring once or twice along the way, until some of the edges of the cauliflower begin to brown. Stir in the currants and continue to bake for about ten more minutes, stirring another time or two, until most of the edges of the cauliflower are browned. Sprinkle with the dill, stir again, and scoop into a serving dish.