Preheat your oven to 180 C. Line a 20cm round cake tin (or bundt tin as I have used in the pictures) with baking paper.
Roughly chop the orange and place into a food processor. Blitz until smooth, around 2 minutes, then add all the other cake ingredients and process until a smooth mixture forms. You may need to scrape down the sides of the bowl a couple of times during this process.
Pour into your prepared cake tin and bake for 30 minutes, or until a skewer inserted comes out clean.
Meanwhile, make the syrup. Pour the juice, rind and sugar into a small saucepan and stir over medium-high heat until sugar dissolves and mixture comes to a boil. Boil for 10 minutes, or until the mixture is thick and syrupy.
Invert cake from the tin and place onto a wire rack with a baking dish underneath to catch any excess syrup. While cake is still hot, pour over the syrup. Allow to sit as the cake absorbs the syrup and cools.
