Preheat the oven to 325°F. Spray three 8-inch round cake pans with nonstick cooking spray. Line the bottoms with parchment paper.

To a large bowl add the graham cracker crumbs, melted butter, sugar, and salt. Mix to combine.

Press 1/3 of the graham cracker mixture into each cake pan. Firmly pressing to create a crust at the bottom of the pan. Bake for 4 minutes. Remove and let cool while preparing the cake batter.

Preheat oven to 325° F. In a medium bowl mix together the cake flour, baking powder, and salt. Set aside.

In a small bowl mix together the sour cream, buttermilk, lime juice, lime zest, and vanilla. Set aside.

In the bowl of a stand mixer fitted with a paddle attachment, beat together the sugar and oil for 2-3 minutes, until they’re lighter in color and well-mixed. Add the eggs, one at a time, beating well after each addition.

With the mixer on low speed, add about 1/3 of the flour mixture, followed by ½ of the buttermilk/sour cream mixture. Add another 1/3 of the flour mixture, the last ½ of the buttermilk mixture, and the last 1/3 of the flour mixture. Mix until all ingredients are combined. Be careful not to overmix!

Divide the batter evenly into the three cake pans, pouring over the graham cracker crusts.

Bake for 28-34 minutes, or until a toothpick inserted into the center of the cake comes out clean or with just a couple crumbs stuck to it. Remove from oven and let cool in the pan for 15-20 minutes, then turn out onto a wire rack to cool completely. If making ahead of time, remove the cake layers from the pans and wrap with plastic wrap and store in the freezer for up to 3 weeks.

In a small saucepan, combine egg yolks, eggs, and sugar. Cook on medium-low heat until the mixture has thickened.

Add the lime juice and zest and cook for a few more minutes, until the mixture has thickened enough to coat the back of a spoon.

Remove from heat and add the butter, one tablespoon at a time and mix until it’s all melted.

Pour the hot curd through a fine mesh strainer to remove any chunks. Cover the curd with plastic wrap and refrigerate until it’s completely cool. This can be made ahead of time and stored in the fridge for up to 4 days.

In the bowl of a stand mixer fitted with a paddle attachment, beat the butter until it’s light and smooth.

Mix in the vanilla bean paste and salt, then slowly add the powdered sugar and cream. Once all the ingredients have been mixed in, beat the buttercream on high for 3 minutes.

Place a cake layer with the crust side ON TOP on a cake board or stand that has a small dollop of buttercream on it. This will help keep the cake from sliding around as you assemble it.

Spread a thin layer of buttercream evenly over the top of the cake layer.

Pipe a rim of buttercream around the top edge of the cake layer to create a dam and add 1/2-2/3 cup lime curd inside the buttercream dam. Be sure to not overfill the cake as it will seep out when you add the next layer and make the cake unstable and difficult to finish icing.

Repeat steps 2 and 3 with the second layer of cake, graham cracker side UP, placing the second cake layer on top of the first layer.

Place the third cake layer on top, graham cracker side UP, and crumb coat the entire cake in a thin layer of buttercream. Refrigerate or freeze for a few minutes, until the buttercream is cold and no longer soft.

Add the final layer of frosting around the entire cake. We made an extra 1/4 batch of buttercream to make the swirls around the top of the cake.

Add additional decorating, if desired, by piping swirls on the top and topping with lime slices and adding crushed graham crackers along the sides of the cake.

You can use lime juice and zest if you’d like. Key limes have a stronger lime flavor, so your lime flavor might not be as strong.

If making ahead of time, remove the cake layers from the pans and wrap with plastic wrap and store in the freezer for up to 3 weeks.

The lime curd can be made ahead of time and stored in the fridge for up to 4 days. If you would like it to be more green, add some food coloring.

If making the buttercream ahead of time, store in an airtight container in the fridge or freezer. Let come to room temperature and beat until light and fluffy.