Step 1

Place the butter, cream cheese, lemon juice, and vanilla in a large mixing bowl, and beat on medium-low speed until smooth.

Step 2

Scrape the bottom and sides of the bowl with a silicone spatula, and add about half the powdered sugar.

Step 3

Stir in the powdered sugar until combined, then scrape the bottom and sides of the bowl again, and add the remaining powdered sugar and the salt.

Step 4

Stir together until combined, then turn the mixer up to medium-high speed and whip until the frosting is fluffy and stiff.  (Be careful not to over-whip the cream cheese frosting, or it could become runny.  As soon as the frosting looks stiff, turn off the mixer and use the frosting immediately.)