1. Melt the butter, sugar and treacle in a saucepan. Once melted turn off the heat and pour in the milk and stir in the raisins (if using). Leave to cool.
2. In the meantime line a 30 cm x 20 cm cake tin with parchment paper and preheat the oven to 150°C/300°F/gas 2.
3. Sift the flour, bicarbonate of soda, ginger and cinnamon together.
4. Pour the melted mixture into the dry ingredients and add the beaten eggs and coconut flakes (if using).
5. Stir well and pour into the tin. Bake in the centre of the preheated oven for 45 mins - 1 hour.
6. Check back after 45 mins to see if the cake is cooked. You can check by inserting a skewer into the centre. It should come out clean. If is doesn't then put back in the oven for another few minutes. If the top starts to brown too much then pop some extra parchment paper on there.
7. Once cooked, remove from the oven and leave to cool in the tin before slicing.