In a large mixing bowl, combine the heavy cream, whole milk, sweetened condensed milk, key lime juice, lime zest, vanilla extract, and salt. Whisk until the mixture is smooth and well blended.
Pour the mixture into an ice cream maker and churn according to the manufacturer's instructions until it reaches a soft-serve consistency.
Transfer the churned ice cream to a container and freeze for at least 4 hours or until firm.
To prepare the chocolate ganache, heat the ¼ cup of heavy cream in a small saucepan over medium heat until it begins to simmer.
Remove the saucepan from the heat and add the semi-sweet chocolate chips. Stir until the chocolate is completely melted and the mixture is smooth.
Once the ice cream is firm, scoop it into bowls and drizzle the chocolate ganache over the top.
Sprinkle the crushed graham cracker crumbs on top of the ice cream and ganache before serving.
