MAKE BASE Microwave sweetened condensed milk and white chocolate in large bowl until chocolate melts, stirring halfway, about 30 seconds. Let cool. Stir in vanilla, salt, and sour cream.
2
WHIP CREAM With electric mixer on medium-high speed, whip heavy cream to soft peaks, about 2 minutes. Whisk one-third of whipped cream into white chocolate mixture. Fold remaining whipped cream into white chocolate mixture until incorporated.
3
FREEZE Place in airtight container and freeze until firm, at least 6 hours or up to 2 weeks. Serve.