Preheat oven to 350 degrees.

Zest two limes and set zest aside. Squeeze 1/2 cup of juice into a measuring vessel or bowl, then muddle the mint leaves in the juice, crushing gently to release the flavor. Set aside and allow the juice and mint to steep.

FOR THE CRUST
In a food processor, add crushed graham crackers and blitz into uniform crumbs. Add the brown sugar and salt and pulse briefly to combine, making sure there are no lumps of either graham cracker or brown sugar. Drizzle the melted butter over the crumbs and pulse until the mixture begins to clump together. Dump into a 9-inch pie plate and use the bottom of a drinking glass to press the mixture firmly and evenly into the bottom and sides. Bake at 350 for 10 minutes, then remove and allow to cool briefly. 

FOR THE FILLING
Strain the minty lime juice and discard the leaves. In a medium bowl or large glass measuring vessel, whisk together the condensed milk and eggs. Add the zest and juice and combine thoroughly. Pour the mixture into the prepared crust and bake at 350 degrees for 15 minutes. Remove and allow pie to cool to room temperature, then refrigerate until fully chilled (at least one hour). 

FOR THE WHIPPED CREAM
In the bowl of a stand mixer (or a medium bowl if using a hand mixer), add the cream and, using the whisk attachment, whip until the cream begins to thicken. With the mixer running, add the sugar in a steady stream, then the vanilla and rum, if using. Continue to whip until the cream stands up in stiff peaks. 

Decorate using the method of your choice:  use a piping bag to garnish decoratively, or simply slather the cream on top of the pie. Garnish with mint leaves and slices of fresh lime. Serve chilled.