For the ice cream, heat the milk gently in a saucepan. Whisk the eggs, sugar and vanilla extract together in a bowl until they are smooth and creamy. Just before the milk comes to the boil, remove it from the heat and whisk a ladleful into the eggs to acclimatize them. Whisk in another ladleful and then pour the eggs and milk back into the saucepan. Turn down the heat to its lowest and cook for a minute or so, whisking all the time, just to cook the eggs through. Remove from the heat, whisk in the cream and pour into a bowl that has a lid. Leave to cool completely, whisking now and then while it cools.
Put the lid on the bowl and put it in the freezer. After an hour, remove the bowl from the freezer and give the mix an energetic whisk with a hand whisk or electric mixer and then put it back in the freezer. Whisk again after another couple of hours. Put it back in the freezer until it is nearly firm.
Meanwhile, make the raspberry purée. Put the sugar, lemon juice and
Swirl the purée through the ice cream with a spoon. Make a few more swirls, folds and pirouettes but not so many that the purée starts to blend in with the ice cream. Cover the bowl again and return to the freezer to set completely.
Alternatively, pour the ice cream mixture into an ice cream machine and churn following the manufacturer’s instructions. When it is ready, transfer to a freezer container and then add the raspberry purée and make your swirls.
Take out of the freezer a few minutes before serving so that it is not rock hard.