Beat the double cream using an electric whisk until it holds its shape. Keep beating on a lower speed and gradually pour in the condensed milk and vanilla extract, then slowly add the lemon zest and juice. Put the mixture in a shallow baking tin or container that will fit in your freezer.
Drop the jam all over the surface in little blobs using a teaspoon, then drag a skewer through the blobs to spread it out a little. Some jam will disappear from the surface but that’s okay. Cover the container and put it in the freezer for at least 3 hrs. This is a soft-set ice cream, so you don’t need to take it out of the freezer too far ahead of serving. Will keep in the freezer for up to three months.
Quick strawberry cheesecake ice creamLeave some strawberry ripple ice cream to soften at room temperate, then quickly stir in some beaten soft cheese, crushed digestives and a little more strawberry jam. Re-freeze before serving.