Preheat the oven to 180°C, fan 160°C, gas 4. Grease a 20cm square cake tin and line with baking parchment.
In a food processor, whizz together the flour, ginger, cinnamon, bicarbonate of soda and butter until it resembles fine breadcrumbs. Set aside.
Put the golden syrup, black treacle, light brown sugar and diced stem ginger in a pan. Heat gently until all the sugar has dissolved, then cook for another minute over a high heat and remove.
Beat the eggs and milk into the syrup mixture, then mix into the flour and butter mixture. Pour into the cake tin and bake for 45 minutes.
Meanwhile, stir the ginger syrup and 2 tablespoons boiling water into the icing sugar until smooth. Remove the cake from the oven and allow it to cool for 10 minutes, then pierce all over with a skewer. Pour over the icing sugar mixture and leave to set before serving.
Cook's tip: if you have leftover slices that are going slightly stale, use them in a gingery version of a bread and butter pudding. Just switch white bread slices with the ginger loaf slices and sprinkle chopped crystallised ginger over them instead of sultanas.