Preheat the oven to 215 F. Line two baking sheets with parchment paper.

Place the egg whites and cream of tartar in a medium bowl or in the bowl of a stand mixer. Make sure the bowl is metal or glass and is very clean. Beat the egg whites on low speed (use the whisk attachment of the stand mixer) until they become frothy.

Gradually add in the granulated sugar, continuing to beat until the meringue forms soft peaks.

Beat the meringue on high speed until it is glossy and forms firm peaks, about 5 minutes.

Transfer the meringue to a large piping bag fitted with a large round tip.

Pipe the meringue into bone shapes on the prepared baking sheets. Since the cake will be between 4-6 inches in height, aim to have the bones be about that long. You can always trim them later.

Bake the meringues for 1 hour or until the bones are dry to the touch and lift easily from the baking paper. If they still are too soft, continue baking for an additional 30 minutes.

Once the bones have baked, turn the oven off and leave the door open slightly. Leave the bones in the oven until they’re completely cool, about 1 hour.

Keep the bones in an airtight container until ready to use.

Preheat the oven to 350 F. Grease cake pans and line the bottoms with parchment paper rounds. Set aside.

In a medium bowl, combine the flour, sugar, baking powder, baking soda, and salt. Add the butter and beat until combined.

Add the eggs, one at a time, beating after each addition. Add the sour cream and beat until smooth.

Add the milk and vanilla extract and beat on medium speed for 1-1 ½ minutes.

In a separate medium bowl, whisk together the cocoa powder and hot water. Add half of the cake batter to the bowl and beat until combined.

Scoop spoonfuls of the two batters into each prepared cake pan, varying their placement in the pan. Aim to have equal amounts of vanilla and chocolate batter. Use a knife to swirl the two batters together and make the marble pattern.

Bake for 30-40 minutes or until a toothpick inserted in the center of each cake comes out clean.

Cool 10 minutes in the pan before transferring cakes to a wire rack to cool completely.

Place the melted butter in a medium bowl and whisk in the black cocoa powder.

Alternately add the powdered sugar and milk and beat until combined and spreadable. Add additional milk if needed.

Stir in the vanilla extract.

Transfer frosting to a large piping bag.

If desired, wrap your cake board in aluminum foil. Place on top of a cake decorating turntable, overturned bowl or plate.

Use a serrated knife to trim the top of each cake so that all of the tops are level.

Place one of the cakes, cut side up, on the cake board. Pipe frosting on the top of the cake and then smooth into an even layer using the off-set spatula.

Place the second cake, cut side down, on top of the first cake. Pipe frosting on the top of the cake and then smooth into an even layer using the off-set spatula.

Pipe lines of frosting around the sides of the cake and then smooth into an even layer using the off-set spatula.

Place the cakes into the refrigerator to chill for 10-15 minutes.

Remove the cakes from the refrigerator. Using a clean off-set spatula, gently smooth the sides of the cakes in small strokes to give the cake a matte feathered texture.

Press the meringue bones into the sides of the cake. If needed, use a sharp knife to trim the bones to fit.

Cut off the top of one of the bones to make a gravestone. Place some of the leftover frosting into a piping bag and use it to write RIP on the gravestone meringue.

Place the Oreo crumbs on top of the cake. Then, place the gravestone meringue and Pluto figure on top.

Store in an airtight container, not in the refrigerator, as the meringues will break down in the refrigerator.