In a large bowl, mix (using whisk attachments) the butter with a hand-held or stand mixer on medium speed until fluffy. Add the powdered sugar one cup at a time until just combined.
Add the lemon juice 1 tablespoon at a time until the desired consistency has been reached. Mix on medium speed for 3 minutes. Add the lemon zest and mix until just combined.
Refrigerate until ready to spread on baked goods.
Notes
SALTED BUTTER – I ALWAYS used salted butter for my baked goods and buttercream frostings, but that is a personal preference. If you wish to reduce the saltiness, go unsalted! Also, make sure your butter is not totally melted. If you don’t have time to bring it to room temperature, microwave it for no more than 30 seconds.
LEMON JUICE – Add the freshly squeezed lemon juice 1 tablespoon at a time until fully incorporated. When you reach the desired frosting consistency, you don’t need to add any more. For a less thick buttercream, you may want to increase the amount of juice used to 4-6 tablespoons. For a thicker frosting, 3-4 tablespoons is ideal.
MIXING – Once you have reached your desired consistency, crank your mixer up to medium-high speed and set a timer for 3 full minutes. Don’t skimp on time. Three minutes of mixing will produce such a super fluffy, creamy and perfect buttercream frosting.
SPRINKLES – Stir in sprinkles at the end for an extra touch of fun! I love doing this when I’m baking treats for kids because…SPRINKLES.