1/2 tsp cream of tartar
125 ml egg white
150 g unsalted butter, at room temperature
75 g Crisco shortening
1 tsp vanilla extract
Using a Bain Marie method, in a mixing bowl combine the sugar with cream of tartar, stir in the egg white (the water bath about 60C). stir the mixture continuously until the mixture reach 50-55C . Remove from the water bath, using a electric mixer, beat on high speed for 5 minutes, lower the speed beat for another 5 minutes, until room temperature and stiff.
In another mixing bowl, cream the butter at medium-low speed, add in the Crisco shortening and vanilla extract until light and fluffy. fold in 1/4 of the meringue into the butter mixture, continue fold in the rest of the meringue.