reaches 215 degrees f, put the second amount of egg whites in a mixer with a whip attachment and whip on high until stiff peaks form.
when the temperature of the sugar syrup reaches 238-240 degrees, or the soft ball stage, remove the pot from heat and slowly stream the syrup into the egg whites, down the side of the bowl while the eggs are still whisking. make sure the syrup does not touch the whisk, or it the sugar will harden on the whisk.
continue whisking on high until the meringue cools down; the bowl should be cool to the tough. add the butter, a piece at a time, while the 