Zest both lemons and set zest aside. Juice one of the lemons to make 2 tablespoons juice. Reserve remaining lemons for another use.
Cream butter and shortening with mixer on medium until light and fluffy. Add lemon zest and juice (and extract if using). Mix well.
Add powdered sugar 1/2 cup at a time and beat until light and fluffy.
To thicken consistency, add more powdered sugar. To soften consistency, add more lemon juice if required.
(Nutrition information provided is an estimate and will vary based on cooking methods and brands of ingredients used.)