I made you a cake!
Just kidding. I made my dad a cake. He had another birthday – which he insists on doing every year, like clockwork – so I decided to make him a cake. I’ve talked about how much he likes key lime pie before. This year I threw in a twist – I made him Key Lime Pie Cake.
This whole cake is built around one key component: the key lime curd. It’s just like this quick & easy lemon curd, but it’s made with key lime juice instead. Once done, it tastes just like the silky sweet and mouth puckering filling of a key lime pie. SO good.
All finished, the cake was lovely. My best cake frosting job to date, if I may toot my own horn. It’s made of two layers of light and tender lime-scented white cake, with a thick layer of key lime curd between them, then frosted with a smooth and rich lime Swiss Meringue Buttercream. To finished it off, I toasted some graham cracker crumbs for the outside because we all know it’s not key lime pie without a graham cracker crust.
I don’t make full layer cakes like this very often because they’re such a project and there usually aren’t enough people around to eat them. That, and the suspense of waiting until the first slice to see if it tastes good just about kills me. What if it’s awful and I’ve just served it to a whole group of people? Yikes.
– When I put the cake together, I was concerned that the wallop of flavor from the key lime curd could be overpowering and too rich when combined with frosting, so I went a little light on the curd. After tasting the cake myself* and harassing everyone who ate it for their opinions, I think I could have used more curd. It was by far the best and most flavorful part of the cake.
– I only used two layers because I had to travel with the cake and I was afraid more layers would not hold up in transit. Next time If I don’t have to travel with the cake, I’d like to try halving each cake layer to make four layers total. That would make room for more curd too!
– By the time we ate the cake, it was a little dry. I think this was due to 3 things: I was careless with measuring and used a little too much flour; I overbaked the cake layers a bit; and the cake sat uncovered in the fridge for a few days before eating. I’ve used this cake recipe before and it wasn’t dry, so I am sure the recipe is not at fault. Next time, I might baste the cake layers with a lime simple syrup just to ensure it stays moist.
* I was sick with the plague (aka a nasty cold) when I tasted this cake, and as such I could barely taste anything. I’m basing my opinions on what little I could taste and what others said about how it tasted.
This cake has several components, most of which can (and should) be made ahead. Final assembly will ideally take place the same day the cake is served, but the cake can be stored in the fridge for up to 2 days.
Prepare key lime curd according to directions below at least one day (up to 3 days) ahead.
Bake cake layers according to directions below. Cool completely before frosting.
Prepare the Lime Swiss Meringue Buttercream according to directions below.
To assemble, place one cake layer (top side up) on a cake plate or board. Place about 3/4 cup of buttercream in a piping bag with a large round tip. Pipe frosting around top edges of cake to create a border of frosting. Fill in center with 1/2 cup or more of Key Lime Curd. Place other cake layer (top side down) on top.
Spread of thin layer of buttercream over top and sides of cake to form a crumb coat. Refrigerate cake for 30 minutes to 1 hour.
Place 1/4 to 1/2 cup of frosting in a piping bag with a star tip. Spread the remaining frosting evenly over top and sides of the cake. Press Graham Cracker Crumble into sides of cake. Spread about 1/2 cup of Key Lime Curd over top of cake, leaving 1/2-inch border. Pipe stars around top edge border.
I made a large batch of curd not knowing how much I would end up needing for final cake assembly. As pictured and described above, I only needed half of the curd for the cake. However, if you plan to make your cake 4 layers you will probably need the whole batch.
This recipe is very easy, but the key is patience. You must cook the curd on LOW heat very slowly and you must whisk constantly. For reference, my electric stove burners range from 1 to 9. I cooked my curd on 3-4 for 10+ minutes.
Preheat oven to 350°F. Spray two 9-inch round cake pans with baking spray.
Whisk together cake flour, baking powder and salt in a small bowl. In a 2-cup measuring cup, first measure out buttermilk, the whisk in egg whites and lime juice.
In the bowl of a stand mixer, beat sugar and zest on low until fragrant, about 2 minutes. Add butter and beat until light and fluffy, about 3 minutes. Beat in vanilla extract. With the mixer on low, add 1/3 of the flour mixture, followed by 1/2 buttermilk mixture. Continue alternating dry and wet ingredients (ending with dry ingredients), beating just to incorporate each new addition. Once all ingredients are added, beat on medium speed for 2 minutes to aerate the batter.
Divide batter evenly between pans. Bake at 350°F for 30-35 minutes, or until toothpick in the center comes out clean. Cool in pans for 5 minutes, then invert cakes onto a cooling rack to cool completely.
Can be made ahead. If making ahead, wrap each layer tightly in plastic wrap and place in a zip top bag. Can be stored at room temperature for a day, or frozen for several weeks.
Preheat over to 350°F. Line a baking sheet with a Silpat or parchment paper.
Break graham crackers into quarters and pulse in a food processor until reduced to fine crumbs. Add salt and brown sugar. With processor running, pour in melted butter. Pulse until mixture resembles wet sand.
Dump mixture onto prepared pan and press mixture firmly to form a flat ‘crust’. Bake at 350°F for 6 minutes. Remove from oven and crumble into pieces with a fork. Return to oven and bake 2 more minutes. Cool completely. Can be made ahead and stored in an air-tight zip top bag until needed.
If you end up making this a 4-layer cake, you may want to make an extra bit of frosting. As is, it was enough for me to frost a 2-layer cake.
Fill medium saucepan with about an inch of water and bring to a simmer. Add egg whites and sugar to the metal bowl of a stand mixer. Set bowl over simmering water and whisk constantly until sugar has dissolved and mixture reads 140°F on an instant read thermometer.
Attach bowl to stand mixer and using the whisk attachment, beat on medium speed until a glossy white meringue with stiff peaks forms and the bowl no longer feels warm to the touch (about 10-15 minutes). Switch to the paddle attachment. Beating on medium-low speed, add butter one piece at a time, letting each piece incorporate before adding the next. Once all butter is incorporated, scrape down sides of the bowl with a spatula. Continue beating for 10-15 minutes until smooth.
Once smooth, add vanilla, lime juice, salt and zest. Beat until smooth.
It’s certainly a beautiful cake. Well done!
I can just imagine the taste – can’t get key limes here in the south of France so will have to use regular limes but I’m sure it’ll be delicious! Am wondering if you have a metric conversion for the cake recipe, I find that weighing rather than measuring gives more consistent results with baking, especially with sponge cakes. Am looking forward to your next recipe!
Regular limes should work just fine if you can’t get key limes. I used a mix of key lime juice and regular lime zest for my cake. I wish I had metric conversions for you! The original cake recipe does not have them, which I’m sure would have prevented me from using too much flour in my cake. If I can find the weight for the flour I will add it to the recipe for future use.
That is truly one of the best looking cakes I’ve ever seen – it must taste absolutely fantastic too.
There’s no way this could NOT taste fantastic! I totally love key lime pie. Making it into a cake was a great idea!
Wow!! This is a stunning cake!! Love it!
Such a pretty cake! I love that you thought to put the graham cracker crumbs on the outside. I bet it would be good with any kind of citrus.
Yum! This looks absolutely delicious! Beautiful photos.
Gorgeous cake! My husband adores key lime. I need to make this for him!
This sounds like a perfect Summer cake, like exactly what I need for my birthday :) My only problem is that by the middle of July I tend to not want to bake anything, but this looks worth it!
“…harassing everyone who ate it for their opinions…” This made me chuckle, because yeah, I do that, too.
What a fantastic cake! It turned out so beautifully and I bet it’s so delicious. Thanks for sharing!
So I made this last weekend. It took quite the effort! But it was sooooo worth it! I’m not sure if the cake worked out correctly, though. I think the cake stayed a bit flat and it tasted a little flowery. That said when put all together it was phenomenal so I WILL try this again and soon!
This looks so incredibly delicious! I can’t wait to try it this summer.
Thanks for this! I made it for a friends shower in cupcake form. I used the curd as a filling and rolled each iced cupcake in the graham cracker crumbles. I finished with a thinly sliced piece if line on top. It got really good reviews!