Cut off and discard any green strawberry tops, then cut all the fruit in half lengthways.
Arrange these on an oven tray lined with unbleached baking paper, then drizzle over the sweetener.
Turn everything together to coat, then spread out the half berries so they have a little space around them.
Roast in a 210C (190C fan)/410F/gas mark 6½ oven for 20-30 minutes, until the strawberries have started to shrivel and caramelise.
Remove, leave to cool, then chill well before using.
Pour the cream into a large bowl, then chill until you are ready to whip.
When you're ready, whip the cold cream to stiff peaks.
Fold in the condensed milk, optional neutral spirit, vanilla extract and salt until just combined, then gently fold in the cold roast strawberries and any syrupy juices from the tray.
Transfer the ice-cream mix to a sealable airtight container, then press a sheet of greaseproof paper directly on to the surface and seal.
Freeze for at least five hours, until solid.
Before scooping and serving, put in the fridge for 45 minutes to an hour, or leave at room temperature for 15 minutes.
