Key Lime Icebox Cake

 

6 limes

4 cups (945g) heavy cream, cold

1 (14-ounce) can sweetened condensed milk

Kosher salt

1 (14-ounce) box graham crackers (about 30 sheets)

½ cup (110g) sour cream

1 tablespoon granulated or powdered sugar

1 teaspoon vanilla extract

 

Zest enough of the limes to have 3 tablespoons zest, then squeeze to have ²⁄³ cup juice. Reserve the remaining limes for garnish. In a large bowl, use a whisk or electric hand mixer to whip 2½ cups of the cream until slightly thickened and beginning to hold its shape. Add the lime juice and zest, then add the condensed milk and a pinch of salt. Continue whipping until the mixture forms soft peaks. Scrape any zest that has collected on the whisk and gently fold back into the beaten mixture. Line a 9 × 13-inch baking dish with a single layer of graham crackers. You may have to break them to fill the entire space. Spoon half the lime cream over the crackers (just eyeball it) and gently spread into an even layer. Top with another single layer of graham crackers, followed by the rest of the lime cream. Add a final layer of graham crackers (reserve any extra) and press down lightly. In the same bowl you used to make the filling, whip the remaining 1½ cups cream, the sour cream, sugar, vanilla, and a pinch of salt until you have medium peaks. Gently spoon the whipped cream over the crackers and spread into an even, swoopy layer. Loosely tent the cake with aluminum foil, then refrigerate for at least 6 hours and up to 2 days. When ready to serve, crush any remaining graham crackers and sprinkle them around the top edge of the cake. Zest some of the remaining limes over the top, then slice the limes and garnish the cake with the slices.