Preheat the oven to 200C/180C Fan/Gas 6. Line/grease an 8″ cake tin.
In a large bowl/the bowl of a stand mixer, combine the butter and granulated sugar on a medium speed until entirely combined. For real creaming, this should be about 3-5 minutes with an electric/stand mixer. Add the eggs, one at a time and combine. Add the orange extract if using.
Add the orange juice (about 40ml) and orange zest and combine again. The mixture may begin to look a little curdled, due to all the citrus/eggs etc, but stick with it!
Combine the flour with the baking soda and baking powder in a small bowl. Add a third of this and a third of the milk, mix until all combined. Then repeat with remaining flour and milk. The mixture will be fairly smooth and should pour easily.
Pour the cake batter into the prepared tin. Bake for 40-45minutes, until golden brown and a cake tester/toothpick comes out clean. Let cool on a wire rack before making the buttercream.
Make the buttercream by first adding the butter to a large bowl and mixing on high until it is light and fluffy. Add the aperol, half the icing sugar and the orange colour (if using). Combine again.
Add the remaining icing sugar and whisk on high, ensuring all is combined. It should be light and creamy, not too thick. Feel free to add more icing sugar to get it to your desired consistency if you like it thicker. Spread over the cake, decorate as you wish, and serve!