Using an electric stand mixer fitted with the whisk attachment, beat the heavy cream, condensed milk, and vanilla extract on HIGH speed (I start out at speed 4 and go to 6 or 8) in a large bowl until thick, stiff peaks form, or for about 7-8 minutes. It’s important to get the stiff peaks (as much as possible). You should after about 7-8 minutes.
Add in the blueberry compote, lemon zest and thyme. Beat until well combined.
Transfer the mixture to a loaf pan or freezer-safe container, cover with plastic wrap and freeze until firm, for at least 8 hours (overnight for the best results) and up to 2 weeks.
When serving, top with more lemon zest and pistachios if desired.