Ingredients
For the Cake:
- 1 cup (2 sticks / 226g) unsalted butter, softened to room temperature
- 2 cups (400g) granulated sugar
- 3 large eggs, at room temperature
- 3 cups (360g) all-purpose flour, sifted
- ½ teaspoon baking soda
- ½ teaspoon baking powder
- ½ teaspoon fine sea salt
- 1 cup (240ml) buttermilk, at room temperature
- ¼ cup (60ml) fresh key lime juice (about 10-15 key limes, or see note)
- Zest of 4-5 key limes (about 2 tablespoons packed)
- 1 teaspoon pure vanilla extract
For the Key Lime Cream Cheese Frosting:
- 1 (8-ounce / 226g) package full-fat cream cheese, softened
- ½ cup (1 stick / 113g) unsalted butter, softened
- 4 cups (480g) powdered sugar, sifted
- 2 tablespoons fresh key lime juice
- Zest of 1-2 key limes for garnish
Note: If you cannot find fresh key limes, you may use regular Persian lime juice and zest. The flavor will be slightly different but still delicious. Do not use bottled key lime juice for the cake batter—it lacks the fresh, vibrant flavor. Save it for a last-resort pinch in the frosting only.
Equipment Needed
- 9×13 inch baking pan or two 9-inch round cake pans
- Stand mixer or hand mixer
- Medium and large mixing bowls
- Zester and citrus juicer
- Whisk and rubber spatula
- Sifter or fine-mesh sieve
- Parchment paper
- Cooling rack
Step-by-Step Instructions
Let’s start with the most important prep work: the limes. I zest all of my limes first, using a fine microplane, being careful not to get the bitter white pith. That bright green zest is pure flavor gold. Then, I roll each lime firmly on the counter under my palm to burst the juice vesicles inside before cutting and juicing them. I measure out the juice I need for both the cake and frosting. Remember, room temperature ingredients are non-negotiable here. Cold butter, eggs, or buttermilk will make your batter curdle and result in a dense cake. I learned this the hard way with a sad, sunken first attempt.(See the next page below to continue steps…)