In a bowl of a stand mixer whisk together the egg whites, sugar and pinch of salt

Heat over a pan of simmering water, make sure the bowl doesn’t touch the water, and whisk constantly until the mixture reaches 160 deg f and feels slippery to the touch.

Immediately place the bowl back on the stand mixer, attach the whisk attachment and slowly raise the speed to high. Whip on high about 7-9 minutes or until the bowl feels cool to the touch. Lower the speed to medium and add in the butter 1 tablespoon at a time until all added in. Mix again on high to fully incorporate the butter and have the buttercream come together. Lower the speed again and add in the Baileys and mix until well incorporated and then mix again on high to bring it back to the right consistency. Remove the bowl from the stand mixer and scrape all the buttercream off the whisk attachment and slowly stir with a spatula to remove air bubbles. It is now ready to pipe or spread on cakes.

Notes : this is half my normal recipe since my normal makes enough frosting for a two layer 9 inch cake or piped on 36 cupcakes.