Make Lemon Cream Frosting by mixing all the ingredients with an electric mixer, adding water at the end as needed in small amounts, until it is a smooth spreading consistency.
This makes slightly more than you need to frost the cookies.
I usually free-hand the frosting amounts and am guessing on measurements, so feel free to adjust amounts as you'd like. If you add too much water, just add more powdered sugar. Frostings like this are very forgiving.
I use an oil-based, alcohol free lemon extract for the frosting, so I can add as much as I want without getting an alcohol taste. If you don't have that, more lemon juice should work if you want to strengthen the lemon flavor beyond a teaspoon or so of extract.