Assemble the ingredients and separate the egg whites from the yolks. Reserve the yolks for another purpose.
Add the egg white and sugar to a large, heatproof bowl (I used the bowl from my stand mixer).
Whisk the whites and sugar together.
Place the bowl over a medium saucepan that has approximately ½" of water in the pan, making sure the water does not touch the bottom of the bowl.
Bring the water to a low boil, whisking the egg whites and sugar continually until the sugar is fully dissolved and the mixture is foamy. *Note - pinch a little of the egg white mixture between your fingers and if it still feels grainy, continue heating until the mixture is completely smooth.
Using the whip of a stand mixer, or a hand mixer, whip the meringue base (starting on low and gradually increasing the speed to high) continually until the mixture begins to thicken noticeably (approximately 3 minutes).
Add the vanilla, cream of tartar, and salt to the bowl and continue whisking on highest speed until soft peaks form.
Using a photo of a skull as a guide, spoon most the Swiss meringue into a general skull shape onto a baking sheet which has been lined with a Silpat sheet. Reserve approximately ½ cup of the meringue for coloring. Set aside.
Use an offset spatula or butter knife to gently shape the skull. You'll want rounded head, square jawline, and pronounced cheeks.
Use the offset spatula or butter knife to carve an upside heart for the nose, two large'ish holes for the eyes, but not carving completely to the bottom of the meringue.
Use the offset spatula to carve away some of the meringue to form chiseled cheekbones and an open mouth that will fit his teeth.
As needed, build up his cheekbones and chin with some of the remaining meringue which has been carved away from other parts of his skull.
Color the reserved meringue with a drop or two of black food gel. Stir well to combine.
Using the offset spatula (or I found that fingers work well for this), gently smooth the colored meringue into the crevices carved for eyes, nose, and mouth.
Cut 4 mini marshmallows in half widthwise and press them into his mouth and gum area.
Gently brush (i.e. wipe) some of the meringue over the marshmallow teeth if desired.
Preheat the oven to 200-degrees and bake the Swiss meringue skull for 5 hours.
Turn off the oven, keep the door closed and allow the skull to cool completely inside the oven.
When the skull is completely cool, remove him from the oven and gently and carefully slide a large spatula under the skull and lift him to a serving platter. *Note - He will be sticky, so spraying the large spatula with baking spray or coconut oil is very helpful.
Blend frozen strawberries with a little bit of water until completely smooth.
Pour the strawberry puree around the Swiss meringue Skull and drizzle some of the strawberry puree directly onto the skull itself for a creepy effect.
Chill until ready to serve. Serve at room temperature or slightly chilled.