Peel and chop the large Russet potatoes into 2-inch chunks. Place the potatoes in a large pot, cover with cold salted water, and bring to a boil over medium-high heat. Cook until fork-tender, about 15-20 minutes, then drain.

Return the potatoes to the pot. Add heavy cream and unsalted butter, then mash until creamy and smooth. Season with salt and pepper to taste.

Mold the mashed potatoes into skull shapes using a skull mold or by hand. Ensure they are tightly packed to maintain shape.

Press cut black olives into the eye sockets for decoration. Optionally, add chives or green onions for hair and detail.

Preheat the oven to 375°F (190°C). Place molded potatoes on a baking sheet lined with parchment paper and bake for 15-20 minutes, until golden and slightly crispy.

Remove from the oven and let cool for a couple of minutes. Garnish with fresh chives or green onions if desired, then serve warm.