Method:
Dissolve espresso powder in water, set aside.
Combine eggs, sugar, vanilla, and salt in bowl of stand mixer.
Place bowl over pan of simmering water (do not let bottom touch water).
Whisk gently until mixture is heated to 160°.
Remove from heat and beat egg mixture at medium-high speed, until light and airy and at room temp.
Add butter, one quarter at a time.
Increase speed to high and beat until fluffy. (if buttercream looks curdled keep whipping)
