Place a 2lb loaf tin in the freezer.

Place the blackberries in a saucepan.

Add the sugar and vanilla.

Warm over a medium heat, stirring regularly.

Bring to a simmer, and cook for 10 minutes, stirring often.

After 10 minutes, remove from the heat.

Carefully mash, with a masher or a fork, until you have a fairly smooth puree.

Place a fine sieve over a large bowl and pour in the puree.

Push through as much as you can, until only pulp and seeds remain, discard these.

Place the puree in the fridge to cool. This could take up to two hours.

When ready, pour the cream and condensed milk into a large mixing bowl.

Whisk on high power for a few minutes until it’s starting to thicken.

Pour in around half of the cooled puree and continue to whisk until you have very thick peaks.

Pour in the remaining puree and carefully fold through.

When there’s a marbled colour effect remove the loaf tin from the freezer and pour in the ice cream mixture.

Spread out, and return to the freezer.

Freeze overnight.