Grease your skull pan with butter. Combine cold butter chunks, flour, egg, sugar, salt, and instant yeast in a bowl. Pour in lukewarm water and mix into a shaggy dough. Knead for 5–7 minutes until smooth, then let it rise for 1-2 hours until doubled.

Deflate risen dough, divide into 8 equal pieces, and press into the skull pan. Let the shaped buns rise for about 1 hour. Preheat oven to 375°F.

Bake the skull pan in the preheated oven for 14-18 minutes until golden-brown. Brush with melted butter after baking and cool completely.

Shape ground beef into skull forms, chill for 30 minutes. Season, then cook patties in a skillet over medium-high heat for 3 minutes per side, adding cheese in the last minute.

Slice open cooled skull buns and place a cheeseburger patty inside each. Add toppings like lettuce, tomato, onion, and pickles. Replace tops and serve warm.