Whip the 2 cups of whipping cream in a mixer (or use a hand mixer) until whipped and fluffy.
In a medium bowl, put together the graham cracker crumbs, melted coconut oil, and optional sugar. Stir it until it combines into a crumble.
Fold in the sweetened condensed milk and key lime juice into the whipped cream. If it gets a little too liquidy - whip up again.
Pour a bit of the cream mixture into an ice cream pail (or parchment lined loaf pan) and alternate with the cream and crumble mixture. Swirl the crumble into the mixture by using a spoon.
Freeze for a minimum of 4 hours, it will still be a little soft at this stage so freeze until preference.