• Preheat the oven to 350 degrees, grease and flour three 8×2 inch round pans.(We also like to add circles of parchment to the bottom of the pans.)
• In a medium bowl, whisk the flour, baking powder, baking soda, and salt. Set aside.
• In another bowl, add the buttermilk, vegetable oil, lime zest and key lime juice.  Set aside.
• In the bowl of your mixer, add the butter and mix at medium speed until smooth. Gradually add the sugar and continue to mix on medium speed for 3 to 5 minutes until lightened in color and fluffy.
• Add the eggs one at a time mixing until the yellow of the yolk disappears.
• With the mixer on low speed, alternately add the flour mixture and buttermilk mixture, beginning and ending with the dry ingredients (3 additions of dry ingredients and 2 of liquid). Mix just until combined (do not overmix).
• Divide batter between three prepared 8 inch cake pans.
• Bake at 350 degrees for 22-24 minutes or until a toothpick inserted in the center comes out clean or with just few crumbs attached. Let cool 10 minutes and turn out.

For the Key Lime Curd

• In a medium sized sauce pan, add the sugar, cornstarch, egg yolks, water, key lime juice, and butter (zest optional). Stir to blend.
• Cook on medium low heat, stirring until ingredients are smooth and well combined. Then, increase to medium high heat and stir constantly as the mixture thickens and starts bubbling. Reduce heat and continue stirring for about a minute more- it is ready when it takes on a pudding-like thickness/consistency. It will thicken more as it cools.
• Remove the sauce pan from the heat.
• Pour the lime curd into a heat proof bowl. Allow to cool 15-20 minutes. Then, lightly press a piece of plastic wrap onto the top of the curd to prevent a "skin" from forming. Refrigerate until cool. The curd will thicken further as it cools.
• When ready to use, remove from the refrigerator and allow to warm a bit and stir for easier spreading. If it has become thicker than you'd like, stir in a small amount of water or key lime juice until combined. .

For the Whipped Cream

• Chill the mixing bowl and beaters/ whisk attachment in the freezer for 10 minutes.
• Pour the whipping cream, powdered sugar and vanilla into the chilled mixing bowl, begin beating on low speed gradually increasing to medium high speed.
• Mix until the cream thickens (approx. 1 ½ minutes) and stiff peaks form. You've reached the stiff peak stage when the beaters can be lifted from the bowl and a peak of whipped cream forms and holds its shape. Be careful not to over-mix.

For the Key Lime Cream Cheese Frosting

• Add the softened butter to the bowl of your mixer, mix until smooth.
• Cut the softened cream cheese into pieces and add to the butter, mixing until blended.
• Add the key lime juice
• Gradually add powdered sugar, mixing on low speed until combined. Gradually increase the speed to medium, mixing until smooth and creamy. Be careful not to over mix.
• This frosting will pipe best if used while still chilled. You can make it in advance, refrigerate and when ready to use let it soften slightly and remix. If the frosting becomes too soft while using just refrigerate the piping bag or bowl for a short while to firm it up.

Assembling the Cake

• Place the first cooled cake layer on the cake plate or pedestal. Using a disposable piping bag with the tip snipped away, pipe a dam about ¼ inch from the edge from the cake layer all the way around.

  **If you don't have disposable piping bags, you could also use a ziplock bag with the corner snipped away. If you don't have either, just allow ½ inch of space between the filling and the edge of the cake so that there is no worry of the filling escaping.
• Next, fill inside of the piped dam with a layer of lime curd followed by a layer of whipped cream. Top with the second cake layer and repeat. Top with the third cake layer. Fill in any gaps between the layers with cream cheese frosting. (I do this with the same bag used to pipe the dam).
• Frost the cake with a thin (crumb coat) of frosting. At this point, we like to freeze the cake for 15 minutes (or chill in the refrigerator for a bit longer) to firm up this first layer of frosting. This step helps to prevent sliding as you decorate.
• Next, add the second layer of frosting. Decorate however you like! I rotated the cake on a turntable and used a cake comb to decorate the sides. I added borders using a 1M (large star) piping tip. I topped it with a sprinkling of lime zest.

Storing the Cake

• Because of the filling and frosting, this cake needs to be refrigerated in an airtight container, under a cake dome, or in a sealed bakery box. However, for the very best texture and flavor, we recommend removing the cake from the refrigerator 2-3 hours before serving. This allows time for the cake and frosting to warm and soften.