Combine milk, cream, sugar, and cornstarch in a medium to large sauce pan, whisking until smooth
Place on medium heat and slowly bring mixture to a simmer, stirring frequently to prevent sticking
Continue stirring until the mixture is thick enough to coat the back of a spoon (10-15 minutes)
Remove from heat and pour into a heat- and freezer-safe container, stirring to begin cooling process
Submerge rinsed mint leaves for 5-7 minutes (keep them on the stems if possible)
Use a slotted spoon to remove leaves from mixture
Cool mixture by placing into a refrigerator for 1-3 hours
Follow your ice cream maker's directions for gelato to freeze or place in a freezer-safe container and into a freezer for 4-8 hours, hand-churning every 30 minutes