Cut the butter into cubes and set aside.
Place the egg white, sugar and pinch of salt in a metal bowl that will nest inside one of your pots. Put about 2 inches of water in the bottom of the pot and bring it to a simmer.
Nestle the bowl of egg whites, sugar and salt on top the pot. You want the bowl to sit just above the water.
Whisk the mixture constantly. This is not something you want to walk away from. Whisking will help the sugar and salt dissolve and keep the egg whites from getting too hot.
Continually whisk until the egg whites have reached 140 degrees F.
This takes only a few minutes so stay by the stove. Use an instant-read or candy thermometer. Once the temperature of the egg whites has reached 140 F. degrees remove the bowl from the pot and use a hand-held mixer in the same bowl or pour the egg whites into the bowl of a KitchenAid stand mixer.
Beat on high until cooled and stiff peaks have formed, about five minutes.
Next, with the paddle attachment if using a stand mixer add ¼ of the cubed and softened butter to the bowl. Beat on high until all of the cubed butter has been incorporated into the meringue. Repeat adding ¼ of the butter to the bowl and beating in until all of the butter has been beat into the meringue.
Add the extract and any gel food coloring you might be using to the bowl and beat on low until beat in.
Increase the speed of the mixer to high and beat the meringue frosting until the frosting is smooth and creamy. It may take from 2 minutes to 5 minutes depending on how soft your butter was.
If frosting cooled cupcakes immediately fit a piping tip on a 16 or 18-inch decorator bag and decorate the cupcakes. Add any sprinkles if using now so they adhere to the softened buttercream frosting.
Refrigerate the frosted cupcakes until serving.