01 - Preheat oven to 320°F. Grease and line an 8-inch square cake pan with parchment paper.
02 - In a large bowl, sift together flour, ground ginger, cinnamon, nutmeg, baking powder, and salt. Set aside.
03 - In a saucepan over low heat, gently melt butter, brown sugar, golden syrup, and black treacle, stirring until smooth. Remove from heat and allow to cool slightly.
04 - Whisk eggs and whole milk together in a separate bowl until combined.
05 - Pour melted syrup mixture into dry ingredients and stir to combine. Add the egg and milk mixture, stirring until smooth and free of lumps.
06 - Fold in the finely chopped stem ginger and 2 tablespoons of its syrup.
07 - Pour batter into prepared pan and smooth the surface. Bake for 45 to 50 minutes, or until a skewer inserted in the center comes out clean.
08 - Allow the cake to cool in the pan for 10 minutes before transferring to a wire rack. Serve warm or at room temperature.