Swiss meringue frosting

Ingredients,
1) 1 cup egg whites
2) 2 cups sugar
3) 2 cups butter
4) vanilla essence

Method:
1) Mix egg whites and sugar in a heat proof bowl and keep it on a double
boiler and whisk until sugar dissolved.
2) or you can even put a can't thermometer in the bowl and when
temperature reaches 140 c remove from heat.at this point be careful
because over temperature will cause your whites cooked.
3) start beating with whisk attachment until stiff peaks forms and
mixture cools completely.
4)at this point start adding butter cubes which should be chilled enough
to hold its shape.
5)when you add butter it starts curdling but don't worry keep beating
until it becomes thick and stiff.
6) use it as desire.