Preheat the oven to 180 C (350 F) then grease a 6-inch cake tin and line the base with baking paper.
In a medium pot, melt the butter, sugar and treacle together over a medium-low heat. Once the butter has melted, remove from the heat.
Mix in the ginger, cinnamon, clove, nutmeg, allspice, salt and pumpkin puree until smooth.
Quickly beat in the egg then fold in the bicarbonate of soda and flour until just combined.
Bake for 35-40 minutes until a toothpick inserted into the centre of the cake comes out clean. Tip out onto a wire rack and leave to cool.