Hull and cut the strawberries in halves or quarters, depending on size.
Put strawberries in a roasting dish, toss with the sugar and roast until juices flow, around 15 minutes. Remove from oven and allow to cool.
Put the cooled strawberries and sweetened condensed milk in food processor and pulse until well combined.
In a separate bowl, whip the heavy cream until it forms stiff peaks.
Carefully fold the cream into the strawberry mixture then transfer to a container suitable for the freezer, cover and freeze. It will need at least 4 hours to be slightly soft-serve, but ideally freeze overnight to be properly frozen.
Notes
Timings don't include cooling and freezing time.See above for ideas to vary the flavor.