No-churn blackberry ripple ice cream

Toast the pistachios in a dry frying pan for a few minutes, until slightly golden and fragrant (or roast them for 5-6 minutes if you are using the oven for another dish). Set aside to cool, then roughly chop. Meanwhile, put the blackberries in a food processor and whizz until smooth. Put a sieve over a bowl and strain the blackberry purée through it, using a wooden spoon to press as much through as possible; discard the seeds.

In a large bowl, use electric beaters to whisk the condensed milk, double cream, mascarpone and a small pinch of salt until thickened and quite stiff (6-8 minutes). Stir 1 tbsp of this mixture into the blackberry purée. Fold most of the nuts through the cream mixture, reserving a few.

Pour ½ the cream mixture into a 900g loaf tin or freezerproof container and ripple through 1/2 the blackberry mixture. Repeat to use up the remaining cream and blackberry mixtures. Scatter over the reserved pistachios. Cover with a piece of baking parchment or a lid, then freeze for at least 6 hours. Take the ice cream out of the freezer 10 minutes before scooping.