This key lime cake recipe is perfect for any person who loves the classic flavors of key lime pie. The tart and smooth curd, moist cake, and ermine frosting work together to give key lime vibes with a beautiful cake presentation. It marries a traditional pie and the beloved cake perfectly.

If you are here because you love all things key lime pie, you won’t beat this recipe.

Key Lime Cake Recipe

This cake is the perfect balance of sweet and tart and makes a beautiful dessert for spring, summer, holidays, or special occasions. If you’re looking for a fresh twist on classic citrus cake recipes, this homemade key lime cake will quickly become a favorite.

Making a key lime flavored cake is a no-brainer, but I’ll share with you my thinking of behind the other two components.

Why Key Lime Curd?

A key lime curd provides the tart flavors one would expect in a traditional key lime pie. Using a combination of Nellie and Joe’s key lime juice, lime zest, and fresh lemon juice gives the perfect zing for the curd filling.

Why Ermine Frosting?

You might be asking, “What is Ermine frosting?” before even wondering why, but I’m going to provide the why first. Your typical American buttercream, while delicious, can be cloyingly sweet. This can be perfect for most cakes.

However, my desire was to try to replicate the whipped cream found in a classic key lime pie. Ermine frosting tends to be super light and fluffy and significantly less sweet than American buttercream. I think it better represents a key lime pie.

While different, ermine frosting isn’t overly complicated to make, which I know readers will appreciate.

So, what is it? Ermine frosting starts with a cooked flour mixture. Flour, sugar, and milk are whisked together in a saucepan and cooked until they thicken into a pudding-like consistency. Once that mixture cools completely, it’s whipped into creamed butter, along with vanilla and a little salt.

The result is a smooth, creamy, and airy frosting that would be the result if an American buttercream and whipped cream had a baby.

For all of my best cake-baking tips, please visit this post.

Key Lime Cake Recipe Card

Key Lime Cake

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Course Dessert

Cuisine Baking

Servings 14 slices

Ingredients

Key Lime Cake

2 1/2 cups Flour
1 tsp Baking Soda
1 tsp Baking Powder
1 tsp Salt
1 cup Sugar
1 cup Sour Cream
1/2 cup Vegetable Oil
1/4 cup Unsalted Butter softened
3 Eggs room temperature
2 Tbsp Nellie & Joe's Key Lime Juice
1 Tbsp Lemon Juice
1/2 Tbsp Lime Zest
1 tsp Vanilla

Key Lime Curd

2 egg yolks
2 eggs
1/2 cup Nellie & Joe's Key Lime Juice
1/2 cup Granulated Sugar
1 Tbsp Lime Zest
2 Tbsp Corn Starch
1/2 Tbsp Fresh Lemon Juice
1/8 tsp Salt
4 Tbsp Unsalted Butter European is best

Ermine Frosting Recipe

2 cups Granulated Sugar
2/3 cup Flour
1 3/4 cup Whole Milk
2 cups Unsalted Butter
2 tsp Vanilla
1/4 tsp Salt

Instructions

Key Lime Cake

Preheat the oven to 350. Prepare two 8-inch cake pans by greasing the sides and coating with a thin layer of flour, tapping the excess off, and discarding it. Line the bottom of the cake pans with parchment paper.
In a large bowl, combine 2 1/2 cups flour, 1 tsp baking soda, 1 tsp baking powder, and 1 tsp salt. Stir to combine completely.
In the bowl of a stand mixer, fitted with the whisk attachment, add 1 1/2 cups sugar, 1 cup sour cream, 1/2 cup vegetable oil, and 1/4 cup softened butter. Whisk until well combined.
Add 3 eggs, one at a time, whisking in between additions.
Add the 2 Tbsp key lime juice, 1 Tbsp lemon juice, 1/w Tbsp lime zest, and 1 tsp vanilla. Whisk until combined.
Switch to the paddle attachment. Add flour, a cup at a time, and beat until completely combined. Start slowly until the mixture begins to become one, and then beat on medium-high until just combined.
Divide the batter among the two prepared pans. Bake for 27-32 minutes, or until the cake springs back when pressed lightly or a toothpick comes out clean.
Allow cakes to cool in the pan for 15 minutes, and then transfer them to a wire cooling rack.

Key Lime Curd

Whisk together 2 eggs, 2 egg yolks, 1/2 cup key lime juice, 1/2 cup sugar, 2 Tbsp cornstarch, 1/2 Tbsp lemon juice, 1 Tbsp lime zest and 1/8 tsp salt in a medium pot. Stir until the cornstarch is dissolved.
Bring the pot to medium-low, stirring constantly for about 6-9 minutes until thickened. It should have a pudding-like consistency.
Remove from heat and immediately stir in butter, stirring until completely melted and smooth.
Place the curd in a fine-mesh sieve and work with a spatula to press the curd through the mesh to remove any lumps and zest.
Cover and cool in the refrigerator.

Ermine Frosting

Whisk 2/3 cup flour and 2 cups sugar together in a medium saucepan over medium heat. Continue cooking the mixture for about 2 minutes to lightly toast the flour, stirring constantly and watching carefully so it doesn’t burn.
Gradually pour in 1 3/4 cup milk while whisking to combine. Increase the heat to medium-high and bring the mixture to a simmer. Keep whisking constantly until it becomes thick and takes on a pudding-like consistency. Once it begins to simmer, continue cooking for an additional minute and then remove from the heat. Make sure to scrape the edges of the pot, as that is where the sugar and flour tend to clump.
Push through a fine strainer if clumps occur or move on to the next step, which is: Transfer the mixture to a jelly-roll pan, using a spatula to spread it thin. Cover with plastic wrap and put in the freezer for 30 minutes to cool. Be sure the mixture is completely cooled before continuing, or it may melt the butter in the next step.
Add 2 cups of softened butter to the bowl of a stand mixer and whip on high speed for 2–3 minutes until it becomes very light and fluffy.
Once the butter is fluffy, transfer the cooled flour mixture into a piping bag and slowly pipe it into the butter while the mixer is running. Adding it gradually helps create a smooth buttercream.
Mix in the 2 tsp vanilla and 1/4 tsp salt, and continue whipping until the frosting is smooth and creamy.

Key Lime Cake Assembly

Level the cakes, and then cut them in half (top to bottom) to create a total of four layers.
Optional: Freeze cakes to lock in moisture and to make it easier to spread the frosting. Add one layer of cake to a cake round. Stack the rest of the cakes on top of that cake with a piece of parchment paper in between. Wrap in plastic wrap. Freeze for 2 hours or up to three months. I almost always freeze my cakes.
Pipe a dam of frosting around the edge of the bottom layer of cake.
Spread 1/3 of the key lime curd in the center of the dam.
Repeat layering.
Cover the top and sides in the ermine frosting and decorate to your liking.