For the topping:
1. Heat the butter in a medium frying pan over a medium heat on the hob. Once the butter has melted, add the apples cut side-down to the pan. Allow to cook over a medium-low heat until the underside is slightly golden and softened (roughly 7 minutes). Flip the apples over and let the other side cook for a further 5 to 7 minutes, until that side is softened.
2. Sprinkle the brown sugar over the base of the cake tin and lay the apple halves on top, cut side down.
For the cake batter:
1. In a large bowl, cream the butter and granulated sugar together until smooth and light. Add the eggs one at a time, beating well between additions. Mix in the chopped stem ginger and yoghurt. In a separate bowl, place the flour, baking powder, bicarbonate of soda, salt, ground ginger and ground cinnamon. Stir with a whisk to combine these dry ingredients then tip into the bowl of wet ingredients. Fold together until just a few streaks of flour remain.
2. Spoon the cake batter into the cake tin and spread out in an even layer. Place in the preheated oven and bake for 45-55 minutes. The cake is ready when a skewer inserted into the centre of the cake comes out clean.
3. Allow to cool for at least 10 minutes before unclipping the wall of the cake tin, flipping the cake over onto a serving plate, then removing the base of the tin and the baking paper from the cake. Decorate with the chunks of crystallised ginger.
4. The cake can be served warm or at room temperature. Store leftovers in an airtight container at room temperature for up to 4 days.
