1. Place the Kerrygold Unsalted Butter in the bowl of a stand mixer and beat at medium speed until smooth, creamy, and pale yellow, about 3 minutes.
  2. Stop the mixer, add about a third of the powdered sugar, and then beat on low until incorporated. Repeat twice with the remaining powdered sugar, stopping the mixer when adding the sugar.
  3. With the mixer on low, add the heavy cream, vanilla, lemon zest, and salt.
  4. Mix until everything is incorporated, then increase speed to medium-high and beat until frosting is smooth and fluffy, about 3-4 minutes.
  5. Add food coloring if using and mix until evenly incorporated
  6. If not using right away or the frosting gets too soft to spread, chill the frosting in the refrigerator and re-whip before decorating.