Key Lime Pie Sheet Cake

This Key Lime Pie Sheet Cake is what happens when two crowd-favorite desserts – classic key lime pie and soft, fluffy white cake – join forces in the best possible way. With its buttery graham cracker crust, tart key lime filling, and creamy whipped topping, it’s a bright and zesty mash-up that works just as well at a summer potluck as it does on a holiday dessert table.

One of my friends told me that his favorite fruit is lime, which I thought was funny at first, but I actually get it. They are so unique and their punchy, tropical citrus flavor is just fantastic, especially in creamy desserts like this key lime sheet cake.

The tiny, tart key limes that grow like crazy down in the Florida Keys have made key lime pie a signature dessert there for more than a century and I did my best to try some every day, often multiple times a day when we visited the Florida Keys. Traditionally made with a graham cracker crust and a creamy, citrusy filling that strikes just the right balance of sweet and tart, it’s a dessert that has stood the test of time.

This fun sheet cake version takes everything we love about the original and gives it a twist: think slab pie meets poke cake, with a fluffy cake layer and a tangy key lime pie filling that soaks right in!

Craving more fresh lime flavor? Dig into my Key Lime Cake, Lime Meltaways, Key Lime Cupcakes, or that classic Best Key Lime Pie.

What You’ll Need

• Graham Crackers – Finely crushed and used for both the graham cracker crust base and the buttery crumb topping.
• Salted Butter – Mixed with graham cracker crumbs to hold the crust and topping together, and also used in the whipped frosting to make it rich and creamy.
• All-Purpose Flour – The foundation of the cake layer, keeping the texture soft and tender.
• Granulated Sugar – Sweetens the cake batter and helps create a light, delicate crumb.
• Baking Powder – Gives the cake rise so it bakes up fluffy and soft.
• Salt – Enhances all the flavors and balances the sweetness in the cake and frosting.
• Egg Whites – Used in the cake to make it extra light and airy without the added richness of yolks.
• Buttermilk & Sour Cream – Added to the cake batter for moisture, tenderness, and a slight tang that pairs perfectly with citrus.
• Vegetable Oil – Helps keep the cake soft and moist, even after it’s been chilled.
• Key Lime Juice & Lime Zest – Packed into the cake, creamy pie filling, and whipped frosting for bold, fresh lime flavor in every bite.
• Clear Vanilla Extract – Adds sweetness and depth without darkening the batter or frosting, keeping things bright and white for a classic look.
• Cream Cheese – Blended with lime juice and sweetened condensed milk to form the base of the creamy, tart key lime pie layer.
• Sweetened Condensed Milk & Heavy Cream – Whipped into the key lime pie filling for sweetness and a fluffy texture, and also used in the frosting to make it smooth and light.
• Powdered Sugar – Used in the whipped frosting to sweeten and give structure to the piped dollops.
• Lime Slices – Totally optional, but they add a pretty finishing touch as garnish right before serving.

How to Make Key Lime Pie Sheet Cake

1. Prep crust base. Preheat the oven to 350°F. In a food processor (affiliate link), pulse graham crackers into fine crumbs until they resemble sand. Add the melted butter and blend until everything is evenly moistened.
2. Form crust layer. Press 3 cups of the graham cracker crust mixture evenly into a 9×13-inch baking dish lined with parchment paper. Set aside and keep the remaining graham cracker crumbs for later.

3. Mix cake batter. In a large bowl, whisk together the flour, granulated sugar, baking powder, and salt. In the bowl of a stand mixer, beat the butter, egg whites, buttermilk, sour cream, vegetable oil, key lime juice, and clear vanilla extract until well combined. Gradually add in the dry ingredients and mix until smooth.
4. Bake cake layer. Pour the cake batter over the graham cracker crust layer in the prepared pan. Bake for 30-35 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean. Once out of the oven, sprinkle 2 cups of the reserved graham cracker crumb mixture evenly over the warm cake. Set aside to cool.

5. Whip cream. In a medium bowl, whip the cold heavy cream using a hand mixer on medium speed until medium-stiff peaks form. Set aside.
6. Make key lime pie filling. In a separate large mixing bowl, beat together the cream cheese, sweetened condensed milk, key lime juice, key lime zest, and clear vanilla extract until smooth and creamy. Gently fold in the whipped cream to create a light, fluffy key lime pie layer.

7. Add more crumb topping. Sprinkle a thick layer of graham cracker crumbs across the cooled cake for extra texture and that buttery crunch.
8. Assemble pie layer. Pour the prepared key lime pie filling evenly over the graham cracker layer, and smooth it out with a silicone spatula. Chill in the refrigerator for at least 8 hours or overnight until fully set.

9. Make whipped frosting. In a clean bowl, beat the powdered sugar, softened butter, heavy cream, lime zest, clear vanilla, and salt until smooth and fluffy.

10. Pipe frosting. Transfer the frosting to a piping bag fitted with a star tip (I like using the 4B tip for this one) and pipe decorative dollops around the top of the chilled cake for a fun but easy border.
11. Garnish and serve. Top with thin lime slices between the piped frosting, a sprinkle of graham cracker crumbs around the edges, and a little extra lime zest for a pop of color and citrus aroma.

Recipe FAQ’s

Tips for Success

• Chill the cake overnight so the key lime pie layer has time to fully set. If you slice too soon, the layers can slide around a bit.
• For nice, clean slices, run a sharp knife under hot water and wipe it off between cuts – or pop the cake in the freezer for 30 minutes before serving.
• Wait to garnish until just before serving. The lime slices can dry out and the graham cracker crumbs won’t stay crisp if they sit too long.
• Clear vanilla helps keep the cake and frosting bright white, but regular vanilla works fine too if that’s what you’ve got on hand.
• Feeding a crowd? This recipe doubles easily – just bake it in two 9×13 pans or a big jelly roll pan.

Substitutions and Variations

• If you can’t find key limes for the zest and garnish, regular limes work just fine. The flavor will be a little different, but still bright and citrusy.
• You can swap Greek yogurt for sour cream in the cake if needed – it’ll still be moist and tender.
• Don’t have clear vanilla? Use regular vanilla extract instead. The cake will have a slightly warmer tone but still taste great.
• Want to lighten it up? Replace the frosting decoration with regular whipped cream instead of buttercream.
• For extra tartness, feel free to add more key lime juice to the pie layer or even the frosting – just taste as you go.
• If you’re short on time, a white boxed cake mix can stand in for the homemade cake layer. The texture will be a little different, but it still works well with the creamy filling.

More Citrus Desserts You’ll Love

• Lemon Blueberry Cake
• Passion Fruit Lemon Loaf Cake
• Orange Loaf Cake
• Lemon Earthquake Cake
• Lemon Layer Cake
• Lemon Bundt Cake