Preheat oven to 430°F (220°C)
Put nectarines in a stove/oven proof pan and sprinkle with sugar
Roast for 30mins
Remove nectarines from oven, turn over in pan, then sprinkle with some of the sugar in the pan. Return to oven and roast for a further 20 mins
Allow nectarines to cool. Remove stones from nectarines and put into a small seperate saucepan. Put cooked nectarines into a high sided bowl and blitz with a hand mixer or briefly in a food processor. You want to break up the fruit, not puree it.
Place blitz nectarines back into pan and put on a low heat. Simmer and stir, working off the caramelised sugar with a spoon or heatproof spatular until it dissolves into the nectarine pure.
Once all sugar is dissolved and mixed in, allow to cool.
Strain nectarine mix and refrigerate until chilled.
In the mean time, add cream to nectarine stones in saucepan. Simmer on a very low heat for about 10 mins. Allow to cool, then strain out the stones.
Transfer to a bowl and mix in sour cream, lemon and salt. Refrigerate until chilled.
If using a using a self chilling churner, turn on the machine 10 mins before churning, otherwise take freezer bowl out of the freezer just before churning.
Mix chilled nectarine mix and cream mix together.
Churn mix in ice cream churner. Takes about 25 mins, depending on your churner. It will be the consistency of soft serve when done.
Serve immediately or if a firmer consistency is preferred transfer to a container and freeze until desired consistency is reached.