Line your slow cooker pot with baking paper. I used a round 3.5 litre slow cooker.
Cream the butter and sugar together until light and fluffy.
Add the eggs one by one and mix in well.
Fold in the flour, ginger, allspice and crystallised ginger until well combined.
Add the golden syrup and mix through.
Pour the mixture into the lined slow cooker pot. Put on the lid and put a tea towel under the lid to catch drips and stop condensation dripping onto the top of the cake.
Cooking time: Depends on your slow cooker and whether it cooks quickly or slowly - I cooked my cake for 1 hour 20 on high then switched to low and continue to cook for 2 hours. Switch to low to prevent the edges burning and then continue to cook until the cake is no longer wet on top. Check regularly and use a skewer or knife to test the cake to see if it is cooked through. Look out for burning round the edges too.
Remove from the slow cooker using the edges of the baking paper and allow to cool.