Step 1: Preheat your oven to 150°C (300°F) and grease a 20cm square baking tin.

Step 2: In a saucepan, melt the butter, golden syrup, and black treacle over low heat. Stir until the mixture is smooth and well combined.

Step 3: In a large mixing bowl, combine the oatmeal, flour, dark brown sugar, ground ginger, and ground cinnamon. Mix well.

Step 4: In a separate bowl, whisk the eggs and milk together. Gradually pour this mixture into the dry ingredients, stirring until fully incorporated.

Step 5: Finally, add the melted butter and treacle mixture to the bowl. Stir until the batter is smooth and all the ingredients are evenly combined.

Step 6: Pour the batter into the prepared baking tin and smooth the surface with a spatula.

Step 7: Bake for approximately 1 hour and 30 minutes, or until the Parkin is firm to the touch and a skewer inserted into the center comes out clean.

Step 8: Once baked, remove the Parkin from the oven and let it cool in the tin for 10 minutes. Then, transfer it to a wire rack to cool completely.