1. Place sponge mix in bowl, blend and water with whisk on slow speed for one minute. Scrape down and mix for further four minutes on medium speed.
2. Transfer to greased tin.
3. Whisk lemon fudge topping with boiling water on slow speed. Scrape down and whisk on high speed for two minutes.
4. Drizzle topping over sponge batter.
5. Bake at 190°C / 375°F / Gas mark 5 for 25-30 minutes or until well risen and golden brown.