Beat soften butter with paddle in a kitchen aid mixer.
Pause mixing and add the powdered sugar. On slow speed mix the frosting slowly.
Once the ingredients are incorporated, increase speed and mix thoroughly. Add vanilla extract, salt, and add half the milk.
If the frosting is runny, add more powdered sugar and if it's too stiff slowly add cream.
Place a dollop of buttercream in a tip and push the frosting through. If there is no definition then add more powdered sugar to the frosting and mix well. Test again and keep adding sugar until you get the right consistency.