1. Preheat oven to 200 °F (about 95 °C). Line a baking sheet with parchment.
2. In the stand mixer (whisk attachment), begin whisking the egg whites for 30 seconds until tiny bubbles appear.
3. Add salt and cream of tartar, then whisk on medium speed for 1 minute until a micro-foam forms.
4. Gradually stream in sugar while mixer runs, allowing it to dissolve before adding more.
5. Continue whisking at medium speed for another 8 minutes until soft peaks form.
6. Add vanilla, then whisk 3 more minutes until stiff peaks hold shape.
7. Transfer meringue to a piping bag with a round tip. Pipe ghost shapes: build a base, then slowly pull upward to form the body, finishing with a little swoop for the head.
8. Bake ghosts for 2½ hours. Then turn the oven off (don’t open!) and leave the meringues inside for 3 hours to fully dry.
9. Once cooled, use a toothpick dipped in black food coloring to dot on “eyes.”

Cake

1. Preheat oven to 350 °F (175 °C). Line three 9‑inch cake pans with parchment and spray lightly.
2. Whisk together flour, cocoa powder, baking soda, salt, and baking powder in a medium bowl.
3. In a stand mixer (paddle attachment), beat together sugar, brown sugar, butter, and oil on medium speed for about 2 minutes until smooth and creamy.
4. Add eggs + yolks, milk, sour cream, and vanilla; mix to combine.
5. With mixer running, gradually add black food coloring until your desired darkness is achieved.
6. Add the dry ingredients, mixing just until nearly combined.
7. Stir in hot coffee and finish combining (batter will thin).
8. Divide batter evenly among the three pans and bake for 25 minutes, or until a toothpick inserted comes out clean or with moist crumbs.
9. Remove cakes and cool completely on wire racks before frosting.

Buttercream & Assembly

1. In the mixer, beat powdered sugar, butter, milk, vanilla, and salt on medium-high until smooth and fluffy.
2. Split frosting into two bowls. Color one bowl purple and the other black (gel food colors give more vibrant hues).
3. Place first cake layer on a cake plate or stand. Spread half the purple frosting evenly.
4. Top with second cake layer and frost with remaining purple frosting. Add the third layer.
5. Frost the top and sides of the cake with black buttercream, smoothing with an offset spatula.
6. Carefully arrange the meringue ghosts atop the cake.
7. Slice into 8–10 generous portions and serve.