Here ya go:
2 liter cream soda
2 tablespoons Butter extract
2 teaspoons rum extract
*drop the extracts into the 2 liter bottle, put on cap and slowly rotate until combined.
1 7oz container of marshmallow creme
1 cup whipping cream
1 teaspoon rum extract
*add all items together in an electric mixer and combine until smooth.
Pour the butterbeer into a glass, drizzle with the cream topping, and enjoy!