Preheat the oven to 200C/400F/Gas 6.
For the filling, peel, quarter and core the apples and cut into large chunks. Place in a shallow ovenproof dish.
Zest and juice the orange, adding the zest and juice to the apples. Mix together with your hands.
Bruise the rosemary sprigs and scatter over the apples. Toss over the blackberries, add a splash of water and scatter over the sugar.
For the crumble topping, place the almonds, flour, polenta, butter and sugar in a food processor and pulse briefly several times, just to mix. The mixture should look like coarse breadcrumbs.
Tip out into a bowl and add a splash of water. Use a spoon to mix briefly - it should be quite clumpy.
Sprinkle the crumble mixture over the fruit.
Place in the oven and bake for 20 minutes.
Turn down the heat to 180C/350F/Gas 4 and cook for a further 20-25 minutes, until the top is nicely browned and bubbling.
Serve with pouring cream or custard.
