a large pastry bag with a medium piping tip (Ateco 803), a 6-inch cake, a 10-inch cake pan, a 6-inch cardboard cake round, a 10-inch cardboard cake round
For the Meringue Bones: Preheat the oven to 175 degrees F. Line 3 baking sheets with parchment paper. Fit a large pastry bag with a medium piping tip.
In the bowl of a stand mixer fitted with the whisk attachment or in a large bowl with a hand mixer, combine the egg whites, cream of tartar and salt. Whisk the whites on medium-high until they start to turn white. Very slowly add in the sugar. Whip the egg whites on high for another 4 to 5 minutes until glossy and stiff peaks form. Transfer to the prepared pastry bag. Pipe the meringue on the lined sheet trays into bone shapes varying in size from 3- to 5-inches-long. You should get about 40 to 50 bones.
Place in the oven and bake for 3 to 4 hours or until completely dried and cooked through. You can break one in half to determine if they are dry all the way through and done. Remove from the oven and let cool. Store in an airtight container until ready to use.
For the Cakes: Preheat the oven to 350 degrees F. Spray a 6-inch and 10-inch cake pan with nonstick cooking spray.
Prepare one box cake mix according to package instructions. Pour the batter into the prepared cake pans, filling them about halfway up the sides. Bake until a cake tester inserted in the center comes out clean, 20 to 28 minutes. Let cool in pan for 20 minutes then remove and let cool on cooling rack. Repeat the process with the remaining boxes of cake batter so you have three 6-inch cakes and three 10-inch cakes.
For Raspberry Blood Sauce: In a medium saucepan combine the raspberries, corn syrup and salt. Bring to a boil over medium heat, then reduce heat to medium-low and let simmer for 6 to 8 minutes. Strain the cooked raspberries through a fine mesh strainer, making sure to press the raspberry pulp to extract as much of the raspberry liquid as possible. Discard the seeds. Let the sauce cool. Once cooled, the raspberry sauce should have the consistency of pancake batter. Whisk in the chocolate syrup to give it a slight darker color to make it resemble blood. Transfer to a resealable container and keep in the refrigerator until ready to use.
For Cream Cheese Buttercream Frosting: In the bowl of a stand mixer fitted with the paddle attachment or in a large bowl with a hand mixer, beat the cream cheese on medium until smooth and fluffy. Add the butter and continue to beat until light and fluffy, another 2 minutes. Add the sugar, one cup at a time. Add vanilla and salt and mix for another 15 seconds. The frosting is easiest to work with at room temperature. If you are not using it right away, transfer it to a reusable container and store in the refrigerator. When ready to use, let it sit on the counter for about an hour and then mix it up again in the stand mixer at medium-high speed until light and fluffy.
To Decorate: Using a long serrated knife, slice the domed top off of each cake layer. Place one of the 6-inch cakes onto a 6-inch cardboard cake round. Using an offset spatula, spread some frosting on top of the cake and place the second 6-inch cake on top. Using a 3- to 3 12-inch round straight-sided drinking glass or round cutter cut out a circle from the center of the 2 stacked cakes and remove the inner cut layers. Crumb coat the cake by frosting it with a thin layer of frosting on all sides and inside the cut out well in the center. Use a little extra frosting inside the well to make sure it is completely coated and sealed. This is where you will add the raspberry blood sauce so it needs to be "watertight”. Place the cake in the freezer for about 15 minutes to allow the frosting to harden.
Place a 10-inch cake on a 10-inch cardboard cake round. Spread some frosting on top and place the second 10-inch cake on top and spread the top with frosting. Place the third cake, cut side down, on top of the second cake to form three layers. Crumb coat the cake by frosting it with a thin layer of frosting on all sides. Place the cake in the freezer for 15 minute to allow the frosting to harden.
Spread some frosting on the cut side (where the dome was removed) of the third 6-inch cake layer. Remove the cakes from the freezer. Smooth out any imperfection in the frosting with your hands. Pour about 1 cup of the raspberry sauce into the well in the center of the layered 6-inch cake to fill it just to the top. Invert the third 6-inch cake layer on top, cut side down to enclose and seal the well. Frost the top layer with a crumb coat and place back in the freezer for 15 minutes to harden. Frost the 10-inch cake so it is completely coated and smooth. Remove the 6-inch cake from the freezer and frost it so it is completely coated and smooth. Carefully place the 6-inch cake on top of the 10-inch cake so that it is centered in the middle to form 2 tiers.
Arrange the meringue bones upright around the outside of each tier of the cake. Decorate the top of the cake with more of the bones and any other edible Halloween decorations like white chocolate skulls. Slice the top tier and remove the slice to allow the bloody raspberry sauce core to pour down onto the bottom tier of the cake. Slice the rest of the cake and enjoy!