Key Lime Cake

This Key Lime Cake is a showstopper for any fans of key lime pie. It’s got all the elements – graham cracker layers, smooth key lime cream cheese frosting, and tart key lime curd all combined with my buttery soft layers of vanilla cake flavors with even more lime zest.

When I was brainstorming summer cake flavors to make for my monthly cake series, I immediately thought of key lime pie cake since I’m a huge fan of it in pie form. When we visited the Florida Keys I tried key lime pie everywhere I could get it, even the chocolate dipped variety, and they were all so good. Obviously I had to turn it into a cake.

I used the reverse creaming method that I have been loving for cakes lately and added fresh lime juice and lime zest for a light citrus-kissed flavor. But to really give the key lime pie vibes, I poured the cake batter over a graham cracker crust for that sweet flavor and texture in every bite.

In my recipe testing, I found that a key lime cream cheese frosting helps replicate the creamy, smooth richness of the pie, but it will still missing that punch of key lime flavor. So I added a fresh citrus curd made with key lime juice, and we had a winner! Don’t be intimidated by the different elements or ingredient list. Each of the pieces is pretty easy and this isn’t any harder than most other desserts.

Doesn’t this just give off total summer-by-the-pool vibes? That’s where you’ll find me with a slice.

What You’ll Need

This is a brief description of some of the key ingredients with an overview of the assembly process. For a printable version with all of the ingredient amounts, scroll to the recipe card below.

• Graham Crackers – You’ll need a couple sleeves for the graham cracker crust and a few reserved crumbs to decorate the cake. Is it even key lime cake without this element? I don’t think so.
• Key Limes or Key Lime Juice – Sure they are smaller and a bit of a pain to zest and juice compared to regular limes, but the flavor is so unique and worth it. You can cheat by purchasing bottled key lime juice and using the zest of regular limes as a shortcut.
• Butter & Oil – I use a combination of salted butter and vegetable oil for the best of both worlds when it comes to cakes. Butter for flavor and oil for unparalleled moisture.
• Cake Flour – Gives the lightest, softest crumb, but you can use regular all-purpose flour as well if that’s what you have on hand.
• Buttermilk – A favorite choice for baking cakes because of the slight tang, richness, and acidity that reacts with the baking soda for soft, light layers.
• Leavening & Flavoring – Baking powder, baking soda, salt, and vanilla are all important players in a cake’s rise and overall taste. Skip them and your layers will likely turn out flat, bland, or both.
• Eggs – These are best used at room temperature for cake layers that bake up even instead of domed. You will also need four egg yolks for the key lime curd.
• Cream Cheese – For best results, I recommend using full-fat cream cheese for the frosting.

Making a Cake Using the Reverse Creaming Method

1. Make graham cracker crusts. Combine graham cracker crumbs, sugar, and butter until evenly moistened and combined. I crush my graham crackers in a food processor (affiliate link) first, then add the other ingredients to make it easy. Divided between three 8-inch cake pans, pressing into even layers, and bake for 8 minutes at 350°F to set the crusts. Set aside.
2. Combine dry ingredients. In a large mixing bowl, add the flour, sugar, baking powder, baking soda, and salt.
3. Gradually add softened butter and oil. With this mixer running on medium-low speed, drop the softened butter into the dry ingredients, one tablespoon at a time. Let it mix in for 20-30 seconds before dropping the next piece. This helps distribute the fat, coating the flour in it and preventing gluten from forming, resulting in a softer, moister crumb. Add the oil after all of the butter has been incorporated.
4. Add wet ingredients. Mix in the buttermilk, eggs, lime zest and juice, and vanilla extract to get a nice smooth batter. Evenly divide the batter between the prepared pans of graham cracker crust.

5. Bake. Bake for 28 to 32 minutes or until a toothpick or skewer inserted into the center of each cake layer comes out clean with just a few crumbs clinging to it.

6. Make the key lime curd. In a medium saucepan, whisk together the sugar, lime juice, lime zest, and egg yolks. Add the butter and cook over medium-low heat, whisking or stirring constantly, until the butter has melted and the curd has thickened enough to coat the back of a spoon, about 10-14 minutes. Pour the curd through a fine mesh strainer to remove any bits of cooked egg yolk or larger pieces of zest and cover with plastic wrap pressed directly against the curd. Cool completely or chill before using.

7. Make the Frosting. Beat the butter and cream cheese together in a large mixing bowl until completely combined and smooth. Add the powdered sugar, lime juice, vanilla, and lime zest, then mix just until smooth and combined. It should be light, fluffy, and spreadable, but do not overmix or the frosting can become runny.
8. Assemble. To assemble, level off the cake layers if needed. Place one layer on a cake plate and spread with a thin layer of the frosting (this helps prevent the lime curd from soaking into the cake layers). Transfer 2 cups of the frosting to a piping bag fitted with a large open tip and pipe a border around the top edge of the cake to create a barrier to hold in the lime curd. Spread half of the lime curd onto the cake and spread it into an even layer. Repeat with the second cake layers, frosting, and remaining lime curd.

9. Finish. Add the top cake layer and frost the entire cake, reserving enough frosting to pipe swirls of frosting around the top edges. I like to do a thin crumb coat, then freeze the whole cake for 20 minutes to help it set up and stabilize the cake when working with a curd filling. Then I do more of a finish coat and press extra crushed graham cracker crumbs into the frosting about ⅓ of the way up the cake for decoration. Pipe frosting swirls around the top using the Wilton 1M tip or other favorite decorative tip and decorate with fresh lime slices for garnish. Freeze the entire cake for 20 minutes or refrigerate 1 hour to help set the frosting before slicing and serving.

Top Recipe Tips

• Use room temperature ingredients. This is my number one tip for cake baking! It helps the batter mix together more evenly and your cake layers won’t dome as much. Plus, the cake will be more moist and tender.
• Don’t overbake. Another common culprit to dry cakes is overbaking the layers. Insert a skewer or toothpick in the center of the cake layers to check for doneness. It shouldn’t be wet, but should still have a few crumbs clinging to it when the cakes are done.
• Level layers before stacking. If you cake layers are rounded (and let’s face it, sometimes they will be), it’s best to use a long serrated knife or cake leveler to even off the tops before stacking, filling, and frosting. Plus, those cake scraps make the tastiest baker’s treat.

Recipe FAQ’s

Substitutions & Variations

• Trouble finding key limes? Using Persian limes (the kind you normally see at the grocery store) will still work if you can’t find key limes or bottled key lime juice, but you’ll want to add a touch more zest and maybe even a combination of half lime and half lemon juice to mimic the complexity of key limes.
• 1.5x or double the frosting. I didn’t want to overwhelm this cake with too much frosting, which would make things much sweeter, but you can see from the images that this amount only gives a thin layer with small swirls on top. Feel free to increase the frosting amounts.

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