In a medium bowl, whisk together room temperature milk and lime gelatin until the mixture is smooth and free of clumps.

Stir in the heavy cream to the milk and gelatin mixture, blending until fully combined. Optionally, add freshly grated lime zest.

Pour the creamy mixture into the Ninja Creami pint container, filling it to the max line and securing the lid tightly.

Place the filled pint container upright in the freezer and freeze for 24 hours.

Remove the container from the freezer and insert it into the Ninja Creami base. Select the 'Ice Cream' setting.

If the sherbet appears crumbly, press the 'Re-spin' button. Add a splash of milk for an extra creamy result if desired.

Scoop the sherbet into chilled bowls or glasses and garnish with a slice of fresh lime or a sprig of mint.