Follow these detailed instructions carefully to ensure your cake is a resounding success from the first mix to the final garnish.

Part 1: Making the Fluffy Coconut Lime Cake

1. Preparation: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans. For extra insurance against sticking, trace the bottom of the pans onto parchment paper, cut out the circles, and place them in the bottom of the greased pans before flouring.
2. Combine Dry Ingredients: In a large bowl, whisk together the sifted all-purpose flour, granulated sugar, baking powder, baking soda, and salt. Whisking thoroughly helps to evenly distribute the leavening agents, which is crucial for an even rise.
3. Cream Butter and Sugar: In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with a hand mixer, beat the softened unsalted butter on medium-high speed for about 2 minutes until it’s smooth and creamy. Add the granulated sugar and continue to beat for another 3-4 minutes until the mixture is light, pale, and fluffy. This process, called creaming, incorporates air into the batter, which is the first step to achieving a fluffy cake.
4. Incorporate Eggs: Add the room temperature eggs one at a time, beating well after each addition and scraping down the sides of the bowl as needed. Wait until each egg is fully incorporated before adding the next. This prevents the batter from curdling. After the last egg is mixed in, beat in the vanilla extract and fresh lime zest.
5. Mix Wet Ingredients: In a separate medium bowl, whisk together the full-fat coconut milk and the sour cream (or Greek yogurt) until smooth.
6. Alternate Wet and Dry: With the mixer on low speed, add the dry ingredients to the butter mixture in three additions, alternating with the coconut milk mixture in two additions. Begin and end with the dry ingredients (Dry, Wet, Dry, Wet, Dry). Mix until just combined after each addition. It is crucial not to overmix the batter at this stage, as it can develop the gluten in the flour and result in a tough, dense cake.
7. Fold in Coconut: Remove the bowl from the mixer. Using a rubber spatula, gently fold in the sweetened shredded coconut. Give the batter a final few folds from the bottom up to ensure everything is well combined without deflating the air you incorporated.
8. Bake the Cakes: Divide the batter evenly between the two prepared cake pans and smooth the tops with your spatula. Bake for 30-35 minutes, or until a wooden skewer or toothpick inserted into the center of the cakes comes out clean or with a few moist crumbs attached. The cake should be golden brown and spring back when lightly touched.
9. Cool Completely: Let the cakes cool in their pans on a wire rack for 15-20 minutes. Then, carefully run a thin knife around the edges of the pans and invert the cakes onto the wire rack. Peel off the parchment paper and let them cool completely to room temperature before frosting. This is a critical step; frosting a warm cake will result in a melted, soupy mess.

Part 2: Whipping Up the Frosting & Assembling

1. Beat Cream Cheese and Butter: In the clean bowl of your stand mixer with the paddle attachment (or a large bowl with a hand mixer), beat the softened cream cheese and softened butter together on medium-high speed until the mixture is completely smooth, creamy, and free of lumps, about 3-4 minutes.
2. Add Sugar and Liquids: Reduce the mixer speed to low and gradually add the sifted powdered sugar, about one cup at a time. Once all the sugar is incorporated, add the fresh lime juice, lime zest, vanilla extract, and a pinch of salt.
3. Whip to Perfection: Increase the mixer speed to medium-high and whip the frosting for 2-3 minutes until it is light, airy, and spreadable. If the frosting is too thin, add a bit more powdered sugar. If it’s too thick, add a teaspoon of lime juice or milk at a time until you reach the desired consistency.
4. Assemble the Cake: Place one of the completely cooled cake layers on your serving plate or cake stand. Spread a generous layer of frosting over the top, about 1 to 1 ½ cups. Carefully place the second cake layer on top.
5. Crumb Coat (Optional but Recommended): Apply a thin layer of frosting over the top and sides of the entire cake. This is called a “crumb coat” and it traps any loose crumbs. Place the cake in the refrigerator for 20-30 minutes to set this layer. This step ensures your final coat of frosting will be clean and crumb-free.
6. Final Frosting: After the crumb coat is set, apply the remaining frosting generously over the top and sides of the cake, using an offset spatula to create smooth sides or decorative swirls.
7. Garnish and Chill: Decorate the top of the cake with toasted shredded coconut and some extra lime zest. For an elegant touch, add a few thin slices of fresh lime. Refrigerate the cake for at least 30-60 minutes before slicing. This helps the frosting set and makes for cleaner slices.