Preheat your oven to 170C / 340F. Grease an 18-inch cake tin with butter or line with parchment paper (you can also make this cake in a 9-inch loaf tin).
In a small saucepan, add butter, sugar, and golden syrup on low heat until the butter melts. Turn off the heat and let the golden syrup mixture cool down for 5-7 minutes then whisk in the egg and the milk.
Next, add flour and lemon zest. Combine well using a whisk to make sure there are no lumps in the batter.
Pour the batter into the cake tin and bake for 45-50 minutes or until fully baked.
Immediately once you get the cake out of the oven, brush it with the golden syrup and sprinkle with shredded coconut. Then let it cool completely before taking it out of the tin.
Notes
Feel free to make this cake in a 9-inch loaf tin if you like.
If you don't have self-rising flour in your pantry, that is fine, you can make your own self-rising flour. Mix 1 cup all purpose flour with 2 tablespoons baking powder. You can double or triple this amount.