Bring butter to room temperature if at all possible. Otherwise you can soften it in a microwave, watching carefully so it doesn't melt.When using the frosting it's best if it's at room temperature. If you have made it ahead of time, take it out of the fridge 30 minutes before using it.I used 1/2 tsp + 1/8 tsp cinnamon, but you can adjust these amounts to suit your taste.It's quickest and easiest to make this frosting with a stand mixer, but you can mix it by hand, just ensure that everything is well combined.