Combine the lemon simple syrup, liqueur and ice in a blender. Blend on the “smoothie” setting or until smooth.
Top with fresh lemon zest and serve immediately.
Zest one of the lemons. Carefully remove the yellow outer skin of the lemon with a knife.
Juice the lemons discarding seeds. If you do not have fresh lemons you can use bottled unsweetened lemon juice.
In a small saucepan bring the lemon juice and sugar to a boil over medium-high heat. Continue to simmer for 10 minutes so the syrup can thicken a bit. Mix in the zest.
Transfer the lemon syrup to a heat proof bowl. Let the mixture sit at room temperature for 20 minutes until cool. Strain out all of the zest. Store in the fridge in a clean airtight glass jar until ready to use.
