In a saucepan, combine granulated sugar, light corn syrup, water, and cream of tartar. Stir over medium heat until dissolved, then increase the heat and boil until the mixture reaches a hard crack stage of 300ºF. Pour the hot mixture onto a parchment-lined baking sheet and let it cool completely for about 2 hours before breaking it into dramatic candy glass shards.

Preheat your oven to 350ºF (175ºC) while you prepare your cake pans. Grease two 9-inch round cake pans with butter, then line the bottoms with parchment paper.

In a large mixing bowl, whisk together the all-purpose flour, cocoa powder, baking powder, baking soda, and salt.

In your stand mixer, cream the softened butter with both granulated and brown sugars until light and fluffy, about 3-5 minutes. Add the eggs one at a time, mixing well after each addition.

Blend in the sour cream, vanilla extract, and vinegar, mixing thoroughly until well combined.

In a separate bowl, combine buttermilk and red food coloring. Gradually add this mixture to the dry ingredients, alternating with the flour mixture, until everything is well blended and smooth.

Divide the cake batter evenly between the prepared pans and smooth the tops with a spatula. Bake for 25-27 minutes or until a toothpick inserted in the center comes out clean.

Allow the cakes to cool in their pans for 10 minutes before transferring them to wire racks to cool completely.

While the cakes cool, whisk together egg whites, granulated sugar, and a pinch of salt over simmering water until the sugar dissolves. Remove from heat and whip the mixture until glossy and cool.

Gradually add softened butter, mixing until the buttercream is smooth and creamy.

Gently heat heavy cream and the white chocolate in a saucepan over low heat, stirring until fully melted and smooth. Stir in a few drops of red food coloring to achieve a bloody effect.

Spread a layer of meringue buttercream between the cake layers, adding dark chocolate shavings. Stack the layers and place the assembled cake in the freezer for about 30 minutes to set.

Frost the outer layer of the cake with the remaining meringue buttercream. Finish by pouring the white chocolate ganache over the top, allowing it to drip down the sides.

Decorate the cake with candy glass shards and any additional ganache as desired.