Beat the Butter: Begin by beating 1 cup of unsalted butter on medium speed for about 1 minute until it's velvety smooth.
Add Flavorings: Once the butter is smooth, add in 2 teaspoons of lime zest, 1 teaspoon of vanilla extract, and a pinch of fine salt.
Incorporate Sugar: Gradually add 4 cups of powdered sugar and 2 tablespoons of fresh lime juice to your mixture while remaining on low speed.
Scrape the Bowl: Occasionally stop to scrape down the sides and bottom of the bowl using a rubber spatula.
Adjust Consistency: Continue beating the frosting on low until it reaches your desired consistency; add lime juice if too stiff or sprinkle in powdered sugar if too thin.
Fix Broken Frosting: If the lime buttercream appears broken or curdled, gently add 1 tablespoon of softened butter at a time.
Stir by Hand: Take a few moments to fold the mixture by hand with a rubber spatula for 1-2 minutes.
Serve and Enjoy: Your Lime Buttercream Frosting is now ready to use!