Preheat oven to 350°F (180°C fan). Grease and line a 9-inch springform pan.
In one bowl, cream the butter and sugar until light and fluffy.
Beat in the eggs one at a time, mixing well after each.
Stir in the flour, baking powder, and vanilla until combined.
Peel, core, and chop apples into small chunks. Fold into the batter.
Spoon the batter into your pan. Sprinkle top with golden sugar if using.
Bake for 45 minutes or until golden and a toothpick comes out clean.
Cool slightly, dust with icing sugar, and serve warm or at room temp.