1. Berry sauce Put the frozen berries in a medium-sized saucepan and heat for a few minutes until they soften, then crush them with a fork. Add the lemon zest, castor sugar and water and cook for 5 minutes until the mixture has thickened and reduced.
2. Layering Whisk the cream cheese until soft and smooth and put in a large dish. Add the yoghurt a little at a time, beating well after each addition to prevent any lumps from forming. Continue until all the yoghurt has been combined with the cream cheese.
3. In a deep glass trifle dish, arrange the Swiss roll slices up the sides and on the base. Add a layer of custard and then the cream cheese mixture.