Cut or tear foil into approximately 3½-4 inch squares (you'll need 12 squares).

Roll each square into a tight little ball.

Preheat your oven to the temperature indicated on your muffin mix package or recipe.

Prepare the muffin batter as directed on your package or recipe.

Place cupcake liners into the muffin pan wells.

Fill cupcake liners with muffin batter about halfway full.

Place 4 foil balls between the sides of each cupcake liner and the walls of the muffin pan wells, creating a "cross" shape around each liner.

Muffins are done when golden brown on top and a toothpick inserted in center comes out clean.

Remove from oven and place pan on wire rack. Let rest in pan for 5 minutes, then gently remove muffins and place on wire rack to cool completely (30-60 minutes).

Cream together room temperature butter and cream cheese on low speed until fully blended and smooth.

Add powdered sugar gradually, allowing each addition to fully incorporate before adding more.

Add vanilla and salt, then continue blending on low for 5-6 minutes until smooth.

Fill piping bag fitted with medium round tip with cream cheese icing. (tip: place piping bag in a tall cup, fold edges over rim like cuffing a sock, fill with icing, then twist top closed.)

Alternatively, fill a ziplock bag with icing and cut a small hole in one corner.

Pipe (or spread with spatula) icing onto each muffin top, following the ghost-like shape created by the foil balls during baking.

Smooth and reshape as needed with a spatula - this "crusting" frosting hardens slightly, making it easier to shape.

Use black decorating gel to create ghost eyes and mouths.