1In a stand mixer fitted with the paddle attachment (hand mixer is fine too) whip the butter on high speed until creamy and light in color, about 5 minutes.
2Add the powdered sugar in two additions, mixing thoroughly for a minute and scraping down the bowl and paddle after each addition.
3Add the lemon juice, whole milk and salt and mix on low until the buttercream is well incorporated and smooth, 1-2 minutes.