01 - In a medium saucepan over medium heat, melt unsalted butter. Incorporate packed light brown sugar and cook for 2 minutes, stirring constantly, until mixture is bubbling and aromatic.
02 - Pour in heavy cream and salt, stirring until mixture is smooth and fully combined. Remove saucepan from heat and integrate vanilla extract.
03 - Return saucepan to low heat. Add whole milk, cream soda, ground cinnamon, and ground nutmeg. Whisk continuously until mixture is hot and steaming, ensuring it does not reach a boil (approximately 5 to 7 minutes).
04 - Taste and modify sweetness or spice according to preference.
05 - Pour steaming drink into mugs. Top with whipped cream and a drizzle of butterscotch or caramel sauce if desired. Serve immediately.