Melt butter and set aside. Crush saltine crackers in a zip-top bag with your hands or a rolling pin until all are similar sized; you don’t want to crush them to dust. Add in sugar and mix until blended, pour in butter and stir with fork or or your hands until the crumbs hold together.

Preheat the oven to 350°F. Pour crust mixture into 9" deep dish pie dish and using your hands, press into bottom and up sides, doing your best to make an even layer. Freeze for 10 minutes, then bake for 12-14 minutes or until just lightly golden, not browned. Remove from the oven and cool while you make the filling.

Pour the sweetened condensed milk, lemon and lime juice, sour cream, lemon and lime zest, and egg yolks into the bowl of a stand mixer with the whisk attachment and mix on low until combined. Stop and scrape the bowl, then increase to medium-high for 3-4 minutes, until the filling has gotten thicker. Scraping the sides again, if needed.

Pour the filling into the par-baked saltine crust and bake in the preheated oven for 15-20 minutes until the filling is set, but still jiggles a little when you shake the pan. You don’t want the top to brown. Allow the pie to cool on a wire cooling rack for 30 minutes, then place in the refrigerator for 4 hours (and up to 12) to fully cool and set.

After the beach pie has fully cooled and set, make the whipped cream. Using a hand-held mixer or stand mixer with the whisk attachment, whip the heavy cream, sugar and vanilla on medium-high until stiff peaks form, about 2-4 minutes. Pipe or spread the whipped cream on top. I used a Wilton 1M. Garnish with lemon and lime slices, extra zest and flaky sea salt, if desired.