01 - Melt unsalted butter in a medium saucepan over medium heat. Stir in packed light brown sugar and cook for 2 minutes, constantly stirring, until the mixture bubbles and becomes aromatic.
02 - Add heavy cream and salt to the saucepan, stirring until a smooth consistency is reached. Remove the pan from heat and blend in vanilla extract.
03 - Return saucepan to low heat. Pour in whole milk, add cream soda, ground cinnamon, and ground nutmeg. Whisk constantly until steaming hot, ensuring the mixture does not boil, approximately 5 to 7 minutes.
04 - Taste and regulate sweetness or spice if preferred.
05 - Distribute the hot butterscotch beverage into mugs. Garnish with whipped cream and a butterscotch or caramel drizzle, if desired. Present immediately.