From America's Test Kitchen Season 8: Lemon Layer Cake
Most versions of lemon layer cake are poorly executed concoctions of heavy cake stacked with filling and frosting that taste more like butter than lemon. We wanted an old-fashioned cake in which tangy, creamy lemon filling divides layers of tender, delicate cake draped in sweet frosting—an ideal contrast of sweet and tart.
Most layer cakes are substantial butter cakes, but we suspected that the light, fresh flavor of lemon would be better served by something more ethereal. After trying a sponge cake and a classic yellow cake, we found that a white butter cake was the perfect compromise: a cake nicely flavored by butter yet light enough for our flavors, with a fine crumb and tender texture. ?Lemon layer cake is often filled with lemon-scented buttercream, but this filling can mute the lemon flavor and make the cake far too rich. We preferred the brightness of lemon curd. We also wanted something lighter than buttercream for our frosting, eventually landing on an old-fashioned classic: seven-minute icing. We needed to make some adjustments, as the traditional version was a little too sweet, slightly thick, and required holding a hand-held mixer for longer than was comfortable. We cut back on the sugar and added a squeeze of lemon juice to solve the first two problems. After some trial and error, we learned that if we heated the mixture to at least 160 degrees and then transferred it to the standing mixer for whipping (rather than holding a hand mixer for seven minutes), the end result was just as billowy and shiny as the old-fashioned version.
Serves 10 to 12
The filling can be made a day ahead and refrigerated, but it will become quite stiff; fold it with a rubber spatula to loosen it before spreading onto the cake. For neater slices, dip a knife into hot water before cutting the cake. Leftovers can be stored covered in the refrigerator, with the cut side of the cake covered tightly with plastic wrap, for up to 3 days.