Grease a skull-shaped mold with butter to ensure the buns release easily. In a large mixing bowl, combine flour, sugar, salt, and instant yeast. Add butter and mix until crumbly. Gradually pour in lukewarm water, stirring until a dough forms. Knead for 5-7 minutes until smooth.

Place the dough in a lightly greased bowl and cover with a kitchen towel. Allow to rise in a warm area for 1 to 2 hours, or until doubled in size.

Gently deflate the dough and transfer to a floured surface. Divide into 8 pieces, shape each into a ball, and press into the greased skull molds. Cover and let rise for another hour.

Preheat oven to 375°F (190°C). Bake the skull molds for 14 to 18 minutes until golden brown.

Shape ground beef into 8 skull-like patties. Season generously with salt and pepper and refrigerate for about 30 minutes.

Heat oil in a skillet over medium-high heat. Add the patties and cook for about 3 minutes on each side until well-browned. During the last minute, place a slice of cheese on each patty.

Slice each bun in half, place a cheesy skull patty on the bottom half, and add toppings. Top with the other half of the bun.