Preheat oven to 175°C (350°F). Grease and flour two 8-inch cake pans. Set aside.

In a large bowl, mix flour, sugar, cocoa powder, baking soda and salt until well combined.

In another bowl, whisk together buttermilk, vegetable oil, eggs and vanilla extract until smooth.

Add purple food coloring to wet mixture. Stir until color is fully blended and consistent.

Gradually add dry ingredients to wet mixture. Mix gently until batter is smooth, soft and lump-free.

Stir in vinegar carefully. It reacts with baking soda to make cake light and fluffy.

Divide batter evenly into prepared cake pans. Smooth tops using spatula for even baking.

Bake for 25 minutes or until a toothpick comes out clean. Avoid overbaking to keep cake soft.

Let cakes cool in pans for 10 minutes. Transfer to a cooling rack and cool completely before frosting.

Beat cream cheese and butter until smooth. Gradually add powdered sugar and vanilla. Mix until creamy.

Place one cake layer on plate. Spread frosting evenly. Place second layer on top and frost entire cake.

Use piping bag to add decorative frosting swirls if desired. Optionally, sprinkle edible glitter or purple sprinkles.

Chill cake for 30 minutes before slicing. This helps frosting set and makes cutting easier.

Cut cake into slices. Serve at room temperature for soft, moist and flavorful bites.