01 - In a large mixing bowl, beat the softened butter and cream cheese with an electric mixer until smooth and creamy, about 2 minutes.
02 - Add vanilla extract, ground cinnamon, ground nutmeg if using, and a pinch of sea salt; mix thoroughly to combine.
03 - Slowly add sifted powdered sugar while beating on low speed until fully incorporated.
04 - Increase mixer speed to medium and beat the mixture for 2 to 3 minutes until light and fluffy.
05 - Add milk or heavy cream one tablespoon at a time until desired spreading consistency is achieved.
06 - Apply immediately on cooled cakes or cupcakes, or cover and refrigerate for up to 3 days. Re-whip before use if chilled.