I started out wanting to make lemon curd out of purely altruistic reasons, but by the end I was scraping every last bit of the bowl to eat off the spoon. As a general rule I find lemon curd too harsh and lemony(!), but this curd is more soothing and custardy than the traditional lemons-only recipe. Now I'm disappointed I have to share it! If you prefer traditional lemons-only curd, then increase the lemon juice to 200ml (4-5 lemons) and the zest of 3 lemons.
This recipe is taken from the book on preserving, I can't recommend this book enough. Not only does it have all of the basic recipes and techniques you would expect from a book on the topic, it also has combinations and variations you wouldn't have dreamed of, as well as several recipes using foraging ingredients (food for free! That's how I got into preserving).
From River Cottage Handbook No. 2: Preserves by Pam Corbin
500g apples (peeled cored and chopped into 1cm pieces)
2 lemons (you need 100ml juice, and all of the zest)
4 eggs (you need 200ml beaten egg)
1. Cook the apples with 100ml water and all of the lemon zest until soft and fluffy. Mash to a purée.
2. Put the apple mixture, lemon juice, butter and sugar into a heatproof bowl over a pan of simmering water. As soon as the butter is melted, pour in the beaten eggs through a sieve, making sure beforehand that the butter mixture isn't too hot (it should be below 60°C). Once the eggs are added, whisk until smooth.
3. Stir the mixture over a medium heat until thick and creamy, which will take about ten minutes. If you have a thermometer then it should reach 82°C but if you don't then judge it by the texture-it should be getting near the texture of lemon curd. It will be slightly softer though as it will set more as it cools.
4. Pour into sterilised jars and seal. It will keep for up to 4 weeks in the fridge.
Read this post for more on preserving and sterilising jars. I use recycled jam jars.