Preheat the oven to 160°C or 320°F. Line your baking tin with baking paper. Grease the sides lightly with butter. This helps the cake release easily after baking and keeps the edges soft and moist.

Place butter, golden syrup, black treacle and brown sugar into a saucepan. Heat gently over low heat. Stir slowly until smooth and melted. Remove from heat and allow the mixture to cool slightly before adding other ingredients.

In a large bowl, combine flour, oatmeal, baking powder, ground ginger and mixed spice. Stir well with a spoon. This step spreads the spices evenly and gives the cake a balanced flavor in every bite.

Pour the cooled syrup mixture into the dry ingredients. Add the egg and milk. Stir gently until everything forms a smooth batter. The mixture will look thick but should still pour easily into the baking tin.

Pour the batter into the prepared tin. Spread evenly using a spoon. Bake for about 50 minutes until firm and golden brown. A skewer inserted in the center should come out mostly clean with a few crumbs.

Let the cake cool completely inside the tin. Slice only after cooling fully. For the best flavor, wrap the cake and store it for one day before eating. The texture becomes softer and richer.