Toast coconut at 350˚F in a small baking pan in oven, stirring a few times, especially towards the end, until golden and dry, 7 to 10 minutes. Set aside to cool.: Warm, nutty aromas will fill your kitchen as the shredded coconut shifts from pale to golden brown, and you will hear a faint crackle as moisture escapes. The even color is your cue that the coconut is toasted without burning; stir several times to prevent hot spots and toasting faster at the edges. Cooling is crucial, because hot coconut will steam against the frosting and become limp; let it cool on a sheet so it crisps up. A common mistake is leaving it in the oven too long, which yields bitter, overcooked flakes, so pull it out at the first sign of even golden color.
Make 4-Ingredient Sponge Cake and set aside to cool. Get the recipe on natashaskitchen. com and be sure to watch the tutorial.: As you mix the sponge, you should notice the batter lighten and develop a smooth sheen, with small airy bubbles forming when properly aerated. The cake bakes into a tender, flexible crumb that slices easily, and cooling on a rack prevents sogginess from trapped steam. This step matters because the sponge provides the soft foundation that soaks up the lime syrup without collapsing. If you rush the cooling, the layers can steam and become gummy, so allow them to cool fully before slicing.
In the bowl of your mixer fitted with whisk attachment, beat together cream cheese and 1 cup sugar on high speed 3 minutes until whipped, scraping down the bowl as needed.: The mixture should transform from dense and pocked to light and airy, with a pale color and silky texture, emitting a subtle tangy scent from the cream cheese . Scrape the bowl periodically to avoid unmixed pockets, and stop once it appears smooth and whipped to avoid overwhipping which can cause a grainy texture. If the cream cheese was not fully softened, you may see lumps, so ensure it reaches room temperature first.
Beat in 16 oz cold sour cream until smooth (1 min on high). Add lime zest and juice and beat to combine (1 minute on high). Refrigerate frosting if not using right away.: Once the chilled sour cream is incorporated, the frosting will become silkier and slightly looser, with a cool, tangy scent. Adding the lime zest and lime juice brightens the aroma immediately; you will smell citrus oils that make the frosting sing. Refrigerating helps it firm so it spreads cleanly, and keeps the texture stable. Avoid adding the sour cream warm or letting the frosting sit out too long, which can make it slump and harder to frost the cake neatly.
In a measuring cup, combine 1/4 cup fresh lime juice, 3/4 cup warm water and 3 tbsp sugar. Stir to dissolve the sugar and set aside.: The sugar should dissolve into the warm water, producing a clear, glossy lime syrup that smells fresh and zesty. This syrup is your moisture agent, so the temperature being warm helps it penetrate the cake layers more evenly. If the sugar feels grainy, continue stirring until fully dissolved, because undissolved sugar will create little crunchy pockets when brushed onto the cake. Use a gentle stream when you brush the syrup so the layers absorb rather than pool on the surface.
Slice cake layers in half with a serrated knife. Place the first layer, cut-side-up on a cake platter. Brush with 1/4 of the lime syrup. Top with a generous amount of cream. Repeat with remaining cake layers then cover the entire cake with remaining cream.: When you slice the layers, the clean serrated motion should leave even, soft edges; if you hear tearing, slow down and saw gently. Brushing the cut side with the lime syrup will produce a faint sheen and you may see the layer darken slightly as it soaks in; this is normal and desirable because it adds both flavor and moisture. Apply the frosting with a spatula in smooth strokes, aiming for even coverage to help the coconut adhere later. A frequent error is using too much syrup at once, which can oversaturate and weaken the layer, so divide the syrup and brush gradually.
Cover the entire cake generously with toasted and cooled coconut flakes, using your hands to scoop coconut onto the sides, pressing gently to adhere. The coconut flakes are crispiest if served right away but it is easier to slice the cake once it's had a chance to set in the refrigerator for about 2 hours.: The tactile act of pressing the cooled toasted coconut onto the frosting is satisfying, and you will feel the flakes stick and settle into the cream. The final look should be uniformly coated with no large bare patches, and you will notice the contrast between the creamy white frosting and the golden coconut. Press lightly so you do not compact the frosting or smear it, and work in small sections to keep control. If you add the coconut while the frosting is too warm, it will slide off, so ensure the frosting is chilled enough to hold the flakes in place. The coconut is at its crispiest when served soon after applying, but chilling for about two hours makes slicing neater and is often preferable for serving.
