In a large mixing bowl, use an electric mixer on medium-high speed to whip 2 cups of heavy whipping cream for about 3-5 minutes until thick, velvety stiff peaks form.

In another bowl, combine 1 can of sweetened condensed milk, ½ cup of freshly squeezed key lime juice, lime zest from about 2 limes, a pinch of salt, and 1 teaspoon of vanilla extract. Mix until smooth.

Gently fold one-third of the whipped cream into the key lime mixture using a spatula. Continue adding the whipped cream in batches and folding carefully to maintain airiness. Fold in half of the crushed graham crackers.

Scoop the combined mixture into a freezer-safe container. Spread it evenly and sprinkle the remaining graham cracker crumbs over the top. Seal and freeze for at least 6 hours or overnight.

When ready to serve, let it sit at room temperature for 5-10 minutes before scooping. Serve in bowls or cones, garnishing with extra lime zest if desired.