¼ cup (56 g) unsalted butter, very soft 3 cups (720 ml) cream ½ cup (50 g) powdered sugar ¼ teaspoon salt 2 large lemons, zested and juiced (about 2 tablespoons zest and ⅓ cup / 75 ml juice) 25 to 30 graham crackers or tennis biscuits, from about 4 sleeves 1 cup (240 ml) Lemon Curd slightly warmed, divided
In the bowl of a stand mixer (or use a large bowl and a hand mixer), whip the butter until very soft. Gradually whip in the cream. When it has been smoothly combined with the butter, add the sugar, salt, and lemon zest. Whip until the cream forms firm peaks, then slowly beat in the lemon juice. Continue beating until completely combined. The cream should still hold soft peaks.
Smear a small spoonful of the lemon cream in the bottom of a 9-by-13-inch (23-by-33-cm) baking dish. Lay down a layer of graham crackers and spoon ¾ to 1 cup (180 to 240 ml) of the whipped cream over the top. Drizzle with ¼ cup (60 ml) of the lemon curd. Repeat three more times, finishing with a top layer of whipped cream. (You will have four layers of graham crackers, and four layers of whipped cream.) Drizzle the final ¼ cup (60 ml) lemon curd over the top of the cake in three straight lines, then draw a knife through these lines perpendicularly, creating a streaked checkerboard pattern.
Refrigerate the cake for at least 2 hours, until the crackers have softened to a cakelike texture (test this by inserting a thin knife along the side and bringing up a few crumbs). This can be made up to 24 hours ahead of time, but it is best consumed within a day or two, as it will get soggy if it sits too long.