Preheat your oven to 350°F (175°C). Lightly grease a 9-inch pie plate with butter or nonstick spray. A glass pie dish lets you see the crust as it browns.

Add the saltine crackers to a large zip-top bag. Press out excess air and crush them with a rolling pin until you have fine crumbs with a few small pieces left for texture, like sand with a few tiny pebbles.

In a medium bowl, combine the crushed crackers and granulated sugar. Pour in the melted butter and mix with a fork until all the crumbs are evenly moistened and clump together when pressed. If the mixture seems too dry, add up to 1 additional tablespoon of melted butter.

Pour the crumb mixture into the prepared pie plate. Use your fingers and the flat bottom of a measuring cup to press the crust firmly across the bottom and up the sides. Bake for 15–18 minutes, until lightly golden and fragrant. Set aside to cool for at least 10 minutes while you prepare the filling.

In a medium mixing bowl, whisk the egg yolks until slightly thickened and lighter in color, about 1 minute. Add the sweetened condensed milk and whisk until completely smooth. Stir in the lemon juice, lime juice, lemon zest, lime zest, and a small pinch of fine sea salt. The mixture will thicken slightly as the citrus reacts with the milk.

Pour the citrus filling into the warm crust and smooth the top with a spatula. Bake for 15–18 minutes, just until the edges are set and the center is slightly jiggly like soft Jell-O. Do not overbake; the custard will finish setting as it cools.

Let the pie cool on a wire rack until it reaches room temperature, about 1 hour. Then cover loosely with plastic wrap or foil and refrigerate for at least 4 hours, or preferably overnight, until fully chilled and sliceable.

When ready to serve, add the cold heavy whipping cream to a chilled mixing bowl. Beat with a hand mixer or stand mixer on medium-high speed until it starts to thicken. Add the powdered sugar and vanilla extract, then continue beating until soft to medium peaks form—creamy and billowy, not stiff.

Spread or pipe the whipped cream over the chilled pie. Garnish with extra lemon and lime zest or very thin citrus slices. Slice with a sharp knife, wiping the blade between cuts for neat pieces. Serve cold.