Preheat the oven to 200°C. Butter and line the base of a 24cm springform cake pan.
To make the base, place flour, caster sugar and butter in a food processor and whiz until you have fine crumbs. Add the egg yolk and continue processing until the mixture comes together in a smooth ball (you may need to add a little chilled water). Wrap in plastic wrap and place in fridge for 30 minutes.
When ready, press the mixture into the base of the prepared cake pan, refrigerate for a further 15 minutes, then bake in the oven for 15 minutes.
Remove from oven and reduce oven temperature to 180°C.
Place the apples, light brown sugar, cinnamon and ginger in a saucepan with 2 tablespoons cold water and cover. Cook over low heat until soft.
Cool, then spread over the pastry base. Sprinkle with the mixed berries.
For the topping, process the flour, butter, demerara sugar, poppy seeds, ground cinnamon, ginger and coriander with 1 tablespoon cold water, until you have a rough crumb mixture. Spoon over the top of the berries, patting down well. Bake for 25-30 minutes, then cool in the pan.
For the berry sauce, place the caster sugar in a saucepan with 1/4 cup (60ml) of water over medium heat. Stir until the sugar dissolves. Add the mixed berries and cook for 2 minutes, breaking the berries up with a spoon.
Allow to cool, then puree in a blender.
If you prefer a smooth sauce, pass it through a sieve.
To serve, cut the crumble cake into slices and drizzle with berry sauce and cinnamon custard (see related recipe).