Get Ready to Bake: Begin by setting your oven to 350°F (175°C). Prepare a 10-inch tube pan by lining it with parchment paper—skip the greasing step for this one.

Whisk Egg Whites: In a clean, grease-free bowl, whisk the egg whites until frothy. Add salt, cream of tartar, and warm water. Slowly incorporate 1 1/4 cups of sugar, adding a tablespoon at a time, and continue mixing until soft peaks begin to form.

Incorporate Flour: Sift cake flour and the remaining 1/4 cup sugar together. Gently fold the flour mixture into the whipped egg whites in small batches to maintain the batter's airiness.

Add Vanilla: Fold in the vanilla extract, taking care not to deflate the batter.

Bake the Cake: Transfer the batter into the lined tube pan. Place it in the oven and bake for 35-40 minutes, or until the cake bounces back when gently pressed. Once done, flip the pan upside down and allow the cake to cool completely before releasing it from the pan.

Prepare the Mixture: In a heatproof bowl set over simmering water, combine sugar, water, and cream of tartar. Add the egg whites and whisk continuously until fully blended and heated through.

Whip to Peaks: Beat the mixture with a handheld mixer or whisk until stiff peaks form, about 7 minutes. Remove from heat and stir in vanilla.

Finish with Coconut: Once spread over the cooled cake, sprinkle with the sweetened coconut flakes.

Frost the Cake: Spread the frosting generously over the cake. Add Topping: Cover the entire cake with the 3 cups of sweetened flake coconut. Lightly press the coconut onto the frosting to ensure it sticks evenly.

Chill and Enjoy: Allow the cake to chill in the refrigerator for about 30 minutes to firm up the frosting before slicing and serving.