Preheat oven to 350°F (175°C). Grease and line a 9x5-inch loaf pan.
In a large bowl, cream together butter and brown sugar until light and fluffy.
Beat in eggs, one at a time, then mix in the orange marmalade.
In another bowl, whisk together the flour, baking powder, salt, and orange zest.
Add the dry ingredients to the wet mixture, alternating with milk. Mix just until combined.
Pour the batter into the prepared loaf pan and bake for 45–50 minutes, or until a toothpick inserted in the center comes out clean.
While the cake is baking, combine glaze ingredients in a small saucepan over low heat. Stir until warmed through and smooth.
Once the cake is done, let it cool in the pan for 10 minutes, then turn out onto a wire rack.
While still warm, spoon the golden syrup glaze generously over the top. Let it soak in slightly before serving.
