In a saucepan over low heat, combine 2 cups heavy cream, ½ cup dark chocolate chips, ¼ cup butterscotch syrup, and 2 tablespoons unsalted butter. Stir continuously for about 5-7 minutes until everything is melted and smooth, allowing the mixture to become velvety and thick. Once combined, remove from heat and stir in 1 teaspoon of vanilla extract to enhance the flavor.

Allow the chocolate mixture to cool for about 5-10 minutes while you prepare the serving glasses. Set out 4 large heatproof glasses, ensuring they are ready to hold your Dark Chocolate Butterbeer.

Pour equal amounts of the cooled chocolate mixture into each glass, filling them about halfway. Then, gently top off each glass with 2 cups of cream soda, pouring slowly to maintain the carbonation. Stir lightly to combine.

For an extra kick, add 1 to 2 ounces of dark rum or bourbon to each glass before topping with cream soda. Stir gently to mix in the alcohol.

Top each glass with a generous dollop of whipped cream and sprinkle with shaved dark chocolate or cocoa powder.

Serve immediately while the drinks are warm or let them come to room temperature if preferred.