Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

Mix Dry Ingredients: In a large mixing bowl, combine the flour, sugar, cocoa powder, baking powder, baking soda, and salt. Whisk together until well combined.

Add Wet Ingredients: Add the egg, milk, vegetable oil, and vanilla essence to the dry ingredients. Mix until smooth.

Incorporate Boiling Water: Carefully stir in the boiling water. The batter will be thin, which is normal.

Bake: Pour the batter evenly into the prepared cake pans. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

Cool: Allow the cakes to cool in the pans for about 10 minutes, then turn them out onto wire racks to cool completely.

Prepare Sugar Syrup: In a small saucepan, combine the sugar and water. Bring to a boil over medium heat, stirring until the sugar dissolves. Allow it to boil until it reaches the soft-ball stage (around 240°F or 115°C).

Whip Egg Whites: In a mixing bowl, beat the egg whites with a pinch of salt until soft peaks form.

Combine Syrup and Egg Whites: Once the sugar syrup reaches the right temperature, carefully drizzle it into the beaten egg whites while continuing to whip. Be cautious not to pour it directly onto the beaters.

Add Flavorings: Continue to whip until the icing is glossy and holds stiff peaks. Then add the vanilla extract and vinegar, and mix until fully combined.

Frost the Cake: Once the cakes are completely cool, spread the boiled icing over the top and sides of the cake.