Combine sweetened condensed milk and white chocolate chips in a large microwave-safe bowl. Heat in microwave at 50% power for 30 seconds. Stop microwave and use rubber spatula to stir mixture.
Heat in microwave at same power at 30 second intervals until white chocolate chips soften. Remove bowl from microwave.
Use rubber spatula to stir mixture, smearing white chocolate chips against side of the bowl, until all the chocolate chips have melted completely.
Stir in sour cream, vanilla, and salt until well combined.
Pour cold cream into second large bowl. Use electric mixer on medium-low speed to whip cream for 1 minute. Increase speed to high and whip until cream is smooth and thick, about 1 minute. Stop mixer and lift beaters out of cream. If cream clings to beaters and makes soft peaks that stand up on their own, you're done. If not, keep beating and checking for 1-2 more minutes. Just don't overwhip the cream.
Use rubber spatula to stir one-third of whipped cream into white chocolate mixture until combined, then gently fold in remaining whipped cream until no white streaks are visible.
Transfer ice cream base to airtight container and press plastic wrap on the surface of ice cream. Freeze ice cream until firm, at least 6 hours or up to 2 weeks. Scoop and serve alone or with your favorite toppings.