Using a paper towel and lemon juice, wipe down the bowls and kitchen utensils that you will use for this meringue, removing all traces of oil.

In the bowl of a stand mixer, combine the white sugar and the egg whites. Set aside.

Place a candy thermometer in the egg mixture and heat the mixture until it is 140 degrees, whisking constantly. This will take 5-10 minutes.

Once the mixture is at 140 degrees, take it off the heat and place it on the base of the stand mixer. Using the whisk attachment, beat the mixture until it is thick, smooth and glossy. This will take 5-10 minutes. The outside of the bowl should feel room temperature to the touch. If it is still warm, let it sit until it cools to room temperature.

Cut the butter into tablespoons.

Take off the whisk attachment and put on the paddle attachment.

Turn the mixer on low speed and add the butter, one tablespoon at a time, allowing each tablespoon of butter to get mixed in before adding the next.

Once all the butter has been mixed in, add the flavoring and beat the buttercream until it is smooth and creamy.

Use the frosting to frost a cake, cupcakes, or cookies. Refrigerate any leftover frosting.