5 egg whites
1 1/4 C sugar
1 1/2 C butter, unsalted, at room temperature, cubed
1 t vanilla
In a metal bowl, whisk the egg whites with sugar, over a pot of simmering water, without touching it.
Whisk until the sugar has dissolved.
Remove from heat and keep whisking with a mixer with a whisk attachment until the mixture is glossy and stiff and the bowl is cool, about 15 min.
Continue mixing with a beater or a paddle attachment. Add butter cube by cube.
Mix until mixture is consistent and back to glossy.
Add vanilla and salt, and mix on low just until incorporated.
Refrigerates for few days in an air tight container if not used same day, or can freeze for up to a month.
Match made in Heaven:
Can use food coloring or add any of these:
Liqueurs, cocoa powder, instant espresso, Nutella, cooled melted chocolate, peanut butter, jam preserves, various extracts, like mint and almond.
Here is the one I use: