Preheat your oven to 350°F (175°C). Grease and flour two 8-inch or 9-inch round cake pans or line them with parchment paper to prevent sticking.

In a large bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt. Whisk to combine.

In another bowl, mix the sugar and vegetable oil until smooth. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.

Add the royal blue gel food coloring (start with 1 tsp) and mix until the color is even.

In a small bowl, mix the buttermilk and vinegar. This helps activate the baking soda for a lighter cake.

Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk-vinegar mixture. Start and end with the dry ingredients. Mix gently to avoid overmixing.

Divide the batter evenly between the pans. Bake for 25–30 minutes, or until a toothpick comes out clean.

Let the cakes cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.

Once cooled, frost the cakes with cream cheese frosting. Spread frosting between the layers, then on top and sides. For extra flair, add colorful sprinkles or edible flowers.