Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners.

In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt.

Add the milk, oil, eggs, and vanilla extract to the dry ingredients and mix until just combined.

Carefully stir in the hot water until the batter is smooth. Do not overmix.

Fill each muffin liner about two-thirds full with batter and bake for 18-22 minutes, or until a toothpick inserted into the center comes out clean.

Let the cupcakes cool in the tin for a few minutes before transferring them to a wire rack to cool completely.

In a large bowl, beat the softened butter with an electric mixer until light and fluffy.

Gradually add the powdered sugar, alternating with milk or cream, beating until smooth and creamy. Mix in the vanilla extract.

Once the cupcakes are completely cool, frost them generously with the vanilla buttercream using a piping bag or an offset spatula.

If using fondant, roll out small circles and shape them into skull-like ovals. If using white chocolate, melt and pipe small skull shapes onto parchment paper, letting them set.

Use a black edible marker or black icing gel to draw simple skeleton faces (eyes and nose holes, jagged mouth) onto the fondant or chocolate skulls.

Carefully place one decorated skeleton head on top of each frosted cupcake.