Sift icing sugar and set aside
Using a standard mixer with a paddle attachment beat shortening for a few minutes to soften and break up. Add butter and beat on low for 5 minutes until incorporated and light.
Beat cream cheese separately for a few minutes to soften and break up. Add to butter mixture and beat on low for 5 minutes.
Slowly add icing sugar on lowest speed to begin to incorporate. Once completely mixed, add vanilla, lemon and salt.
You can now use to decorate cakes or cupcakes. If you would like a firmer mixture leave in the fridge to firm up.