Creating Key Lime Cake is straightforward if you follow these simple steps:

1. Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
2. Mix Dry Ingredients: In a large bowl, whisk together the flour, baking powder, baking soda, and salt.
3. Cream Butter and Sugar: In another bowl, beat the softened butter and granulated sugar until light and fluffy.
4. Add Eggs: Add the eggs one at a time, mixing well after each addition.
5. Incorporate Buttermilk: Mix in the buttermilk, key lime juice, lime zest, and vanilla extract until fully combined.
6. Combine Mixtures: Gradually add the dry ingredients to the wet mixture, stirring until just combined. Do not overmix.
7. Divide Batter: Pour the batter evenly into the prepared cake pans.
8. Bake: Place in the preheated oven and bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
9. Cool: Remove from the oven and let the cakes cool in the pans for 10 minutes. Then, transfer to wire racks to cool completely.
10. Prepare the Frosting: In a large bowl, beat the softened butter until creamy. Gradually add powdered sugar, alternating with key lime juice, and mix until smooth. Stir in lime zest and vanilla extract.
11. Assemble the Cake: Once the cakes are completely cooled, place one layer on a serving platter. Spread a layer of frosting on top. Place the second layer on top and frost the top and sides of the cake.
12. Decorate: Optionally, garnish with lime slices or additional lime zest for a beautiful finish.

These steps will guide you in creating this incredible cake effortlessly.