In a medium bowl, stir together graham cracker crumbs, melted butter, and sugar. Spread crumb mixture onto a sheet pan.
Bake for 15 minutes. Let cool; break into pieces. Set aside.
In large bowl, stir together cream, condensed milk, and lime zest and juice. Freeze for 1 hour.
Pour mixture into an ice cream maker, and churn according to manufacturer’s instructions for 12 to 15 minutes. Transfer to a metal or glass container. Wrap tightly in plastic wrap, and freeze for at least 4 hours or overnight.
To serve, top with graham cracker pieces. Garnish with zest, if desired.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/key-lime-ice-cream/