This is best done in a stand mixer, with a candy thermometer. The standing mixer must be very clean and dry. If it has any butter or oil, the eggs will never beat correctly.

Put the sugar and cream of tartar into a heavy saucepan.

Add the boiling water, and turn the flame to medium-high. Place the thermometer so it is in the syrup, but not touching the bottom of the pan.

While the syrup is coming to a boil, beat the egg whites in the standing mixer. Using the whisk attachment, beat the eggs on high until they have formed very stiff peaks and are glossy in appearance.

Check the syrup. Add the extract, It will come to a rolling boil, and then simmer down all on its own. When it has stopped bubbling, check the thermometer. it should have reached 240 degrees or the softball stage. Immediately remove from the heat, and take it over to the stand mixer with the eggs in it.

With the mixer beating on high, slowly, and carefully pour the syrup into the eggs, beating constantly. Continue beating for about 3 minutes, or until the frosting has cooled down a bit.

Decorate your cake or cupcakes as desired.