Preheat the oven to 350°F (175°C) and spray three 8-inch round cake pans with non-stick cooking spray.

In a large mixing bowl, whisk together cake flour, granulated sugar, baking powder, coarse kosher salt, and ground ginger.

In a separate bowl, whisk together eggs, egg whites, whole milk, apple cider vinegar, light brown sugar, melted unsalted butter, vegetable oil, and vanilla extract until smooth.

Gently fold the wet ingredients into the dry ingredients until just combined; avoid overmixing.

Divide the batter evenly into the prepared cake pans and tap gently to remove air bubbles.

Bake for 21-25 minutes or until a toothpick comes out clean; cool in pans for a few minutes before transferring to a wire rack.

Beat the softened unsalted butter until creamy, then gradually add powdered sugar, cocoa powder, meringue powder, and salt until fluffy.

Once completely cooled, frost the top of one layer, stack and repeat until all layers are frosted.

Melt chocolate candy melts in a microwave-safe bowl, fill skull molds with melted chocolate, and freeze until firm.

Remove chocolate skulls from molds and place on top of the frosted cake.