Preheat the oven to 180°C/350°F/gas Move the ice cream to the fridge so it starts to soften.,

Crack the eggs into a mixing bowl, add the sugar, and whisk until pale, fluffy and at least doubled in size.,

Sift in the flour and slowly fold it through with a spatula.,

Grease a baking tray (roughly 26 x 36cm) with butter, then line it with greaseproof paper and grease that too.,

Spoon half your sponge batter on to the tray, blobbing it about in different places, then sift the cocoa powder into the remaining batter and fold it in.,

Spoon the chocolatey sponge into the gaps on the tray, and use the spoon to drag it through the white sponge in S-shapes and circles until it looks beautiful and marbled. Make sure there are no gaps.,

Place the tray on the middle shelf of the oven and bake for 12 to 15 minutes, or until cooked through.,

Grease another large sheet of greaseproof paper with butter and sprinkle over a few good pinches of sugar.,

Take the sponge out of the oven and confidently flip it over on to the paper. Peel and discard the top piece of paper, then, while the sponge is still warm and flexible, loosely roll it up into a long sausage, including the paper, and leave it to cool for around 20 minutes.,

Once cooled, gently unroll the sponge and spread over half of the jam.,

Take big dessert spoons of your soft ice cream and randomly distribute them over the sponge, leaving the last 5 or 6cm at one end free of filling so that it creates a seal when you roll it up.,

Dollop over teaspoons of the remaining jam, then sprinkle your bashed-up chocolate bar all over. Use a spatula to smear everything into a fairly smooth dense layer.,

Start rolling the sponge up again, making sure there's no paper inside it. If the filling starts to slip out, just push it back in. Twisting the ends and squeezing it into a long, fairly even ice-cream sausage.,

Pop it into the freezer for 3 hours, and take it out around 5 to 10 minutes before you want to use it so it thaws enough to slice.,

Unwrap your arctic roll, take a slice out of each end to expose the frozen insides, and serve with fresh summer fruits tossed in lemon juice and a pinch of sugar, or any edible flowers if you have them.