Get Ready to Bake: First, preheat your oven to 350°F (175°C). Then, lightly spray a 9" x 13" baking pan with non-stick spray, ensuring it's ready for your delicious cake.
Mix the Cake Batter: In a spacious mixing bowl, beat together the softened butter and granulated sugar until the mixture becomes light and fluffy. Next, add the eggs one at a time, beating well after each addition until fully incorporated.
Add Wet Ingredients: Gently stir in the milk, vanilla extract, fresh lime juice, and 2 teaspoons of lime zest into the butter-egg mixture until everything is just combined.
Combine Dry Ingredients: In a separate bowl, whisk together the all-purpose flour, baking powder, and salt. Gradually add these dry ingredients to the wet batter, mixing on low speed with an electric mixer until smooth and well-blended. Be careful not to overmix!
Bake to Perfection: Pour the prepared cake batter evenly into your greased baking pan. Bake in the preheated oven for 25 to 30 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Cool Completely: Once baked, remove the cake from the oven and place it on a wire rack to cool down completely in the pan. This step is important for achieving a perfect frosting application later!
Whip Up the Frosting: While your cake cools, it's time to make the creamy, tangy frosting. In a medium bowl, beat together the softened butter and cream cheese with an electric mixer until they are smooth and light.
Add Lime Goodness: Stir in the 4 tablespoons of fresh lime juice and 2 teaspoons of lime zest into the butter and cream cheese mixture, blending until evenly distributed.
Sweeten It Up: With your mixer on a low speed, gradually add the confectioners' sugar, one cup at a time, until the frosting becomes smooth, creamy, and wonderfully spreadable.
Frost and Garnish: Once the cake is completely cool, spread the luscious lime frosting evenly over the top. For a final touch, garnish with additional fresh lime zest to enhance both the flavor and appearance.