When I was growing up, my grandmother, Nanny, regularly made her Lemon-Lime Refrigerator Sheet Cake. Basically, you cooked a Duncan Hines lemon cake, poked holes in it with a fork once baked, poured liquid lime jello on top and then spread a frosting made of instant lemon pudding, whipped topping mix and cold milk over it. Then your put it in the fridge until nice and cold. The result was a psychedelically-hued green and yellow cake that was cool, creamy and yummy in a simple, not overtly lemony or limey way (you can see a bit of this cake in the photo behind my udpated version).
I wanted to modernize that cake because a) I like to use real ingredients with no weird additives and/or fake flavors, and b) I like to cook from scratch. So, I found a lime cake recipe from Bon Appetit 2009 and adapted this cake from that.
It's intensely limey, intensely lemony and really pretty scrumptious. I hope you like it! —em-i-lis
In a small bowl, whisk together the lime zest, lime juice and 1/4 c sugar. Set aside. In a separate small bowl, whisk together the lemon zest, lemon juice and remaining 1/4 c sugar. Set aside.
For the cake
Preheat oven to 350°F. Butter and flour 8-inch square baking pan.
Using electric mixer, cream butter and 1.5 c powdered sugar in large bowl. Beat in eggs 1 at a time. Beat in milk, then flour. Transfer batter to prepared pan; smooth top. Bake cake until tester inserted into center comes out clean, 25 minutes.
Once you remove the cake, use a skewer or fork to poke holes all over it. Pour the lime syrup you'd set aside evenly over the top of the hot cake. Let cool.
When the cake is cool, whisk the remaining 1 cup powdered sugar into the lemon syrup; drizzle over cake. Grate lemon and lime zest over the top if you like. It looks pretty!
Let the cake stand 1 hour, then cut into squares.