Hazelnut Buttercream

This classic buttercream frosting turns out juicy and luxurious. Tom Douglas will sometimes add whipped cream for a lighter flavor.
In a blender or food processor, whisk together the powdered sugar. Transfer the sugar to a medium heatproof bowl and whisk with the egg whites and salt. Place the bowl over a saucepan of boiling water and beat gently until the sugar is completely dissolved, 5 minutes.Transfer the warm egg-white mixture to the bowl of a stationary electric mixer fitted with a whisk. Add the vanilla and beat on medium-high speed until the cream is thick and shiny, about 8 minutes. Beat the butter a few bites at a time, making sure that it is completely absorbed before adding more. The buttercream should be light and fluffy; if it feels runny at any time, put the bowl in the freezer for 5-10 minutes, then return it to the mixer and continue to beat.Whisk together the hazelnut and praline paste until smooth, scraping off the sides and bottom of the bowl. Remove the bowl from the mixer and beat with a wooden spoon to remove any air bubbles.