Make the filling first. It benefits from sitting in the refrigerator for a while before baking.

In a large glass bowl (don't use metal), whisk together the egg yolks, 2 teaspoons of the lime zest, and the salt. Whisk in the sweetened condensed milk and the lime juice. Put the filling in the refrigerator while you make the crust.

In a medium bowl, combine the gingersnap cookie crumbs and the melted butter, blending with a fork to make sure the butter is distributed evenly through the cookie crumbs. Press into a standard 9-inch pie pan. Place in the refrigerator.

Preheat the oven to 350.

Bake crust for 8 minutes, just until it begins to give off a fragrance. Remove from oven and let cool slightly. (You can make the crust a day ahead of time, if you like.)

Reset the oven temperature to 325. Pour the filling into the baked crust.

Bake 15-20 minutes, until the center is just set. Don't overbake.

Cool on a rack. When the pie is barely warm or room temperature, transfer it to the refrigerator.

Just before you're ready to serve the pie, combine the heavy cream and the confectioner's sugar in the bowl of a stand mixer. Whip until the cream has reached stiff peaks.

Spoon the sweetened whipped cream into the center of the pie in an attractive mound, leaving some of the light-green custard visible around the periphery. Sprinkle the remaining 1 teaspoon lime zest over the whipped cream.