Preheat your oven to 350F. Line a cupcake pan with 12 foil or paper cupcake liners. In a medium bowl, beat together the butternut squash, oil, sugars, buttermilk, and vanilla. In a separate bowl, sift together the flour, baking soda, baking powder, salt, and spices. Add the flour mixture into the wet ingredients in two parts, gently mixing on low just until combined – be sure not to overmix! Pour 1/4 cup of batter into each cupcake liner (approximately 2/3 full). Bake for 20-22 minutes; insert a toothpick into the center of a cupcake – if it comes out clean, they’re done! Remove from oven, and allow to cool in the pan for five minutes. Transfer the cupcakes to a baking rack, and cool completely before frosting.

In a medium bowl, cream the butter until it is light and fluffy, approximately two minutes. Add in the marshmallow creme and vanilla extract, and continue to beat until incorporated. Gradually add in the powdered sugar until the mixture is thick and fluffy. Add frosting to a large pastry bag.

Temper the white chocolate, and pour into molds. Place in the refrigerator to harden. Place 2/3 of the graham cracker crumbs into a sandwich bag with a small amount of brown gel food coloring. Gently knead and rub the bag to incorporate the color into the crumbs. Repeat with the remaining 1/3 of the crumbs and green gel food coloring.

Use a small paring knife or cookie cutter to remove the center of each cupcake. Using a pastry bag, pipe a generous amount of frosting inside each cupcake. Replace the centers of the cupcake (you may need to trim them down to get them to fit). Add a small amount of the frosting to the top of each cupcake, using a spatula to smooth out. Roll the tops of the cupcakes into the brown graham cracker crumbs, and sprinkle the green crumbs around the edges, to resemble dirt and grass. Un-mold each white chocolate skull, and place on top of the cupcake, adding additional frosting and crumbs to the top and side of the skull.