Line a large baking sheet with parchment paper; set aside.

Combine all of the ingredients in a medium saucepan. Place pan on the stove over medium-high heat, and stir the mixture until it comes to a boil.

Once it begins to boil, stop stirring and allow it to continue boiling. As soon as a candy thermometer reaches 300ºF, turn off the heat and immediately pour the candy liquid onto the baking sheet. Use a heat resistant spatula or a spoon, to spread the candy liquid out toward the edges and into an even sheet. Let sit and harden for 2 hours.

Once the sheet of candy is completely solid, use a hammer to carefully break it up into pieces. Be careful during this step.

Preheat oven to 350ºF. Line four 6-inch round baking pans with parchment paper, and spray with nonstick cooking spray.

In a mixing bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt until combined; set aside.

In the bowl of a stand mixer fitted with a paddle attachment, beat the butter and sugars together on medium speed until pale and fluffy. Beat in the eggs, one at a time, until combined, scraping down the sides and bottom of the bowl as needed. Beat in the sour cream, vanilla, and vinegar on medium speed.

Pour the dry ingredients into the wet ingredients and mix until combined. Whisk the food coloring into the buttermilk, then pour it into the batter. Mix until just combined, scraping down the sides and bottom of the bowl as needed.

Divide batter among the four cake pans. Bake for 25-27 minutes or until a toothpick inserted in the center comes out clean. Allow to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

Combine the egg whites, sugar and salt in the bowl of a stand mixer. Remove bowl from mixer and place over a simmering pot of water. Whisking constantly, heat mixture until sugar is dissolved and the temperature registers 150-160°F on a candy thermometer, about 3 minutes.

Secure whisk attachment onto stand mixer, and beat the egg white mixture on high speed until cooled to room temperature and fluffy. Add the butter, one piece at a time, and continue beating until smooth and creamy. If the mixture looks curdled, that’s totally normal--just keep beating until it becomes smooth and satiny.

Add the vanilla and continue beating for about 30 seconds.

Place the white chocolate and heavy cream into a microwave-safe bowl. Heat in the microwave for 30 seconds, remove and stir until smooth. If you still see bits of unmelted chocolate throughout, heat for another 15-20 seconds.

Stir in the red food coloring, followed by just a teensy tiny bit of black food coloring (if using). Allow ganache to cool and thicken slightly for about 30 minutes.

Place a layer of cake onto a cake plate or pedestal. Top with a layer of buttercream, then use a cheese grater to grate a bar of dark chocolate evenly over the buttercream. Top with another layer of cake, and repeat steps until the top layer of cake is added. Place in the freezer for 30 minutes to stabilize cake for easier frosting.

Once chilled and solid, frost the entire cake with a crumb coat, then return to the freezer until frosting has hardened. Add another layer of frosting, making sure that there is no cake peeking through the frosting.

Starting with the sides, pour the ganache along the top perimeter of the cake. Once the sides are done, fill the center in with ganache.

Take your "glass shards" and stick them into the center and sides of the cake. Pour more ganache onto the shards, if desired.