Place the butter, dark brown sugar, black treacle and golden syrup in a saucepan. Heat gently, stirring, until melted and smooth. Remove from the heat and allow to cool for 10 minutes.
Preheat the oven to 180°C (160°C fan). Grease and flour a Bundt tin or prepare a silicone mould.
In a large bowl, mix together the flour, baking powder, ground ginger, cinnamon and mixed spice.
Pour the cooled treacle mixture into the dry ingredients and stir gently until combined.
Beat in the eggs one at a time, mixing well after each addition.
Gradually add the milk and stir until you have a thick, smooth batter.
Pour the batter into the prepared tin and level the surface.
Bake in the centre of the oven for 45–55 minutes, or until a skewer inserted into the cake comes out clean.
Leave the cake in the tin for 10 minutes, then carefully turn it out onto a wire rack to cool completely.
Dust with icing sugar before serving.