To make cake, preheat oven to 350 degrees and spray 3 9-inch cake pans with baking spray with flour. (Or butter pans and then lightly coat with flour.)
In a large mixing bowl (one that fits an electric mixer) combine flour, sugar, cocoa powder, baking soda, and salt.
In a medium bowl, whisk together buttermilk, vegetable oil, eggs, and vinegar.
With the mixer on low, add the buttermilk mixture to the flour mixture. Once all buttermilk mixture has been added, turn to medium speed and beat until smooth.
Add food coloring and beat until mixed evenly.
Divide batter evenly between the prepared pans and bake about 22 to 25 minutes. Let cool in pans for 10 minutes and then remove to wire rack to cool completely.
For frosting, beat cream cheese and butter with an electric mixer until smooth. Gradually beat in confectioners' sugar.
Spread frosting between layers of cakes and on top and sides. If you are having trouble with red crumbs from the cake showing through the frosting, spread a thin layer of frosting to cover the cake and place the cake in the refrigerator until the frosting firms up. Then go back and put a thicker layer of frosting on. Refrigerate cake to firm up frosting before adding bloody ganache.
Melt white chocolate bark with cream cheese in a heavy-bottomed pan over low heat, stirring continuously.
Once melted, add food coloring to get desired color. Drizzle on top of cake to resemble blood.