Preheat and prepare the tin: Preheat the oven to 140°C (275°F). Line a 9x9 inch square tin with greaseproof paper.
Mix dry ingredients: In a large mixing bowl, sieve 250g of self-raising flour. Add a pinch of salt, 2 teaspoons of ground ginger, and 250g of fine oats (or medium oatmeal). Mix together with a wooden spoon.
Melt wet ingredients: In a small saucepan, combine 120g of light brown muscovado sugar, 150g of unsalted butter, 200g of black treacle (or dark molasses), and 100g of golden syrup. Place the pan over low heat and melt the ingredients while stirring well.
Combine mixtures: Once fully melted, carefully pour the wet mixture into the flour mixture and stir until well combined. The mixture will be quite thick.
Add milk and egg: In a separate bowl, whisk together 150ml of semi-skimmed milk and 1 large egg. Gradually add this milk mixture to the cake mixture, stirring well between each addition. The mixture should loosen up.
Bake the cake: Transfer the cake mix to the lined tin and spread it evenly across the base. Place the tin in the center of the preheated oven and bake for about 1 hour, or until a skewer inserted in the center comes out clean.
Cool and serve: Once cooked, remove from the oven and allow the parkin to cool completely in the tin. This will help it hold its shape. Once cool, transfer to a wire rack and slice into 16 square pieces. Enjoy!