1. Wash and destalk the blackcurrants, place in a saucepan and cover with 250ml water. Bring the mixture to the boil and simmer for 20 minutes, until the skins of the currants are soft and the liquid has almost evaporated. 
2. Add the lemon juice and sugar, then cook the jam until the mixture reaches 105C on a sugar thermometer. 
3. Leave to cool for a few minutes then pour into hot, sterilised jars and seal immediately. 

To make the roll 

1. Preheat your oven to 200C/fan 180C/gas 6. Grease the base of a 33cm x 23cm Swiss roll tin with your preferred grease of choice! Cut a piece of greaseproof paper to fit in the base of the tin and brush with some more butter or oil. 
2. In a bowl, whisk together the sugar and eggs until pale and thick. 
3. Sift half the flour into the mixture and carefully fold it in. Repeat with the other half of the flour. It’s essential to do this gently to make sure your sponge is light and fluffy. Once the flour is combined, fold in 1tbsp of lukewarm water. 
4. Pour the mixture into the prepared tin and use a spatula to smooth it out so it is spread evenly. Bake for 10-12 minutes in the middle of the oven, until golden. Meanwhile, take your lovely homemade jam and give it a good mix to loosen it up before spreading. 
5. Take a clean, damp cloth and lay it on the work surface. Place a piece of greaseproof paper that is larger than the sponge on top of the cloth. Dust the greaseproof paper with the icing sugar. To loosen the sponge, run a knife around the edges they transfer onto the dusted greaseproof paper. Peel the paper off the base of the sponge and trim the edges of the sponge to neaten it up. 
6. Spoon heaps of jam onto the sponge, leaving a small border around the edge. 
7. Score a line, across the short edge of the sponge, about 1cm from the edge. While the sponge is still warm, begin to roll, using the scored line to help with the first turn. Use the paper to help roll the sponge tightly. Let it cool before serving.