Lots of Lovely Layers: Key Lime Pie Layer Cake

I took a short break from my fresh yeast baking projects to make a birthday cake for my friend Dorothy. As usual, she gave me wide latitude in deciding what to make, but she did request something with a lot of layers. Being on furlough meant that I had as much time as I needed to make a cake, so I decided to take on a project with a somewhat high level of difficulty: the "Key Lime Pie Layer Cake" from Christina Tosi's All About Cake. The cake incorporates no fewer than five subrecipes: graham cracker cake; sour cream frosting; graham crumbs; key lime curd; and graham buttercream. The upside is that all of the subrecipes can be made in advance.

It so happens that I had made two of the five components before. A few weeks prior when I was improvising a s'mores birthday cake for my friend Jim's daughter McKenna, I made the graham crumbs and graham buttercream and added them to a devil's food cake with toasted marshmallow buttercream. The previous time I made the buttercream I had a difficult time getting it to emulsify into a thick consistency. This time I decided to see what would happen if I tried mixing it with an immersion blender. It worked out beautifully.

I made the key lime curd before baking the cake so that it would have time to chill before I assembled the cake. I'm pretty sure this is the first time I've made citrus curd where the recipe requires a blender. You start out by mixing sugar and key lime juice in a blender until the sugar has dissolved. Then you add eggs and blend until the mixture is bright yellow. You transfer the lime mixture to a pot and cook it over low heat until it starts to boil and thicken. Then you transfer it back to the (cleaned) blender; add bloomed gelatin, butter, and salt; and blend until the mixture is thick and shiny. After putting the curd through a sieve I put it in the fridge until I was ready to assemble the cake.

I am getting better at making Christina Tosi's cakes as I get more practice, and I didn't have any problems with the graham cracker sheet cake. I actually pulled out my digital timer to make sure that I mixed the batter for the amount of time specified in the recipe; a total of more than fifteen minutes of mixing is required. You cream softened butter with sugar until and fluffy; add eggs one at a time beating after each addition; slowely drizzle in a mixture of buttermilk, key lime juice, and oil; beat until the mixture has doubled in size and is very light in color; and incorporate the dry ingredients (cake flour, ground graham crackers, baking powder, and salt). You pour the mixture into a parchment-lined 9-inch by 13-inch pan and bake.

The final component, the sour cream frosting, was the easiest to make. You cream softened butter with powdered sugar and salt until fluffy, and slowly add a mixture of sour cream and lemon juice. You whip the frosting until it's silky and holds medium peaks.
Once I had all of the cake components ready, assembly was fairly straightforward. All of Tosi's layer cakes require a minimum of twelve hours of time in the freezer to set up, followed by three hours of defrosting in the fridge before serving. So I assembled the cake a day ahead of time. I used a 6-inch cake ring as a guide to cut out three rounds of cake from the sheet of graham cracker cake (one of the rounds was two semi-circles fitted together). Then I fit a cardboard cake circle inside the cake ring and lined it with a strip of acetate.

I put one of the cake rounds inside the ring and brushed it with key lime juice. Then I spread on sour cream frosting, followed by graham crumbs and a layer of lime curd. I added the second layer of cake, brushed it with lime juice, and repeated the layers of frosting, crumbs, and curd. After adding the final cake layer, I covered it in graham buttercream and topped the cake with more graham crumbs before popping the cake in the freezer.
The next day I took the cake out of the freezer, pushed the cake out of the ring and removed the acetate, and let the cake defrost in the fridge. I loved the tall proportions of the cake and the individual slices. The cake was decadently delicious. To be honest, I don't remember much about the flavor of the actual cake. But the cold, creamy, tart lime curd and the crunchy, buttery graham crumbs were amazing. I loved all of the different flavors and textures in every bite. Making this cake required quite a bit of effort, but the results made it entirely worthwhile.

Recipe: "Key Lime Pie Layer Cake" from All About Cake by Christina Tosi.

Previous Post: "McKenna Turns Ten!: S'mores Cake," March 18, 2019.

Previous Birthday Cakes for Dorothy: Caramel Cake with Salted Caramel Frosting (2018); White GĂ©noise with Raspberry Cloud Cream (2017); Bananas Cake 2.0 with Cream Cheese Frosting (2016); Whipped Brown Butter and Vanilla Birthday Cake (2015); Lemon Mousse Cake with Fresh Raspberries (2014); Antique Caramel Cake (2013); Grasshopper Cake (2012); Restaurant Eve Cake (2010).


Sue Kelly said…
I’m in the process of making this cake for my son’s birthday. I’ve had some trouble so I’ve been searching for other people’s experience. My first problem is that my graham crumbs aren’t crunchy. They’re very tasty but not crunchy. My second problem is the graham buttercream is sooooo runny. I’ve precisely measured in grams with a digital scale. It’s all salvageable but sadly not what I had hoped for. I’m a bit envious that you seemed to have no problems and I’m wondering where I went wrong?
Hi Sue! I don't have any independent memory of the process of making this cake, but as I noted in this blog post and the linked post about the s'mores cake, I actually did have trouble with the graham buttercream, both times! The first time I just kept adding butter. The second time I used an immersion blender on it, which fixed the problem right away. So I would recommend an immersion blender (or if you don't have one, you could try a food processor). I didn't have any problem with the crumbs, though, and I don't recall having any problem with Christina Tosi's crumb components in her other recipes. All I could suggest is a little more time in the oven, and making sure that the crumbs are completely cooled before you store them. Good luck, and happy baking!
Sue Kelly said…
Thank you for your reply! I missed the part about using the immersion blender. I will put a note in my book and try that next time. Thank you! My graham crumb issue remains a mystery. I will try them again sometime and perhaps use a slightly higher oven temp. The cake is now in the freezer. The components all taste good so I’m hoping for a good outcome. Thanks again!