Preheat oven to 300°F (150°C).
Line an 8-inch tin with parchment paper.
Mix oatmeal, flour, ginger, and baking powder.
Add salt and brown sugar to the mix.
Melt butter, treacle, and syrup in a saucepan.
Stir until smooth, then cool slightly.
Beat egg and milk together in a bowl.
Pour egg mixture into dry ingredients.
Add melted butter mixture, stir well.
Pour batter into the prepared tin.
Bake for 1 hour until firm and springy.
Cool on a wire rack before slicing.