In a small saucepan, bring 1 cup of water to a boil.
In a separate bowl, combine the softened butter, brown sugar, ground cinnamon, ground nutmeg, vanilla extract, and a pinch of salt. Mix until fully incorporated.
Once the water reaches a boil, remove it from the heat and pour it over the butter mixture.
Stir vigorously until the butter has melted and the ingredients have blended into a smooth mixture.
Taste and adjust sweetness by adding more brown sugar if desired.
Pour into a mug and top with whipped cream if using.
Notes
Serve in a cozy mug, sprinkle a little extra nutmeg on top of the whipped cream for added flair, and garnish with a cinnamon stick for stirring.