Preheat the oven to 200C/400F/Gas 6. To make the crumble topping, put the flour and brown sugar in a large bowl and mix well. Taking a few cubes of butter at a time, rub them into the flour mixture until it resembles breadcrumbs.
Sprinkle the mixture onto a baking tray in a thin layer, using two sheets if necessary. Bake in the preheated oven for 5-6 minutes, or until lightly golden brown. Remove from the oven and break with a fork, then return to the oven and repeat the process a couple of times, until you have a lovely crunchy biscuit topping. Set aside; if continuing to cook the apple crumble immediately, leave the oven on.
To make the filling, heat a wide, shallow, heavy-bottomed pan and melt the butter until it foams. Add the star anise and cook over a low heat until the butter is flavoured with the star anise. Add the apples, sugar and cinnamon (if using), and cook, stirring frequently, until the sugar has dissolved and the apple is soft at the edges. Remove the cinnamon (if using) and the star anise, and add a little bit more sugar if you like.
To assemble, butter a medium-sized ovenproof dish. Spoon the fruit mixture into the bottom, then sprinkle the crumble mixture on top. Ensure the oven is preheated to 200C/400F/Gas 6, and bake for 20 minutes until the crumble is browned and the fruit mixture bubbling. Leave to cool slightly.
To serve, put some crème fraîche into a small bowl and top with some pomegranate seeds. Serve alongside the crumble.