Pre heat the oven to 170℃ and prepare your round tin.
In a bowl place the sugar and self raising flour.
Quarter the orange and place in your food processor or Nutribullet (skins and all) along with the melted butter and eggs. Blitz until smooth.
Pour the orange mixture into the dry ingredients and combine using a dough whisk.
Pour into the prepared tin and cook for 35 minutes until a skewer comes out clean.
Allow to sit in the tin for 10 minutes before tipping onto a wire rack to cool.Ice once cool.