Preheat the oven to 180C. Grease and line a 22cm round cake pan.
Using a electrical beater, cream the butter with sugar until light and fluffy
Beat in eggs, one at a time, beating well before each addition, if necessary adding a spoonful of flour with the last egg to prevent mixture from curdling.
Beat in orange zest. Add the flour all at once and mix well, then slowly mix in the orange juice.
Scrape the batter into the prepared pan and bake in the preheated oven for 45-50 minutes or until skewer inserted into the center of the cake, comes out clean. If it starts to brown too quickly, cover loosely with a sheet of lightly greased aluminium foil.
Leave the cake in the pan to cool on a wire rack, then unmold and serve.
Convert to US measurements using this conversion tool.
Rum is optional but do use it for deeper flavor.