Preheat oven to 350°F (180°C) and line baking sheets with parchment paper or a silicone baking mat.

Using a stand mixer fitted with the paddle attachment, combine the butter, sugars, egg, lemon zest, and limoncello and beat on medium speed until creamy and free of lumps.

In another bowl, combine the flour, baking powder, and salt. Mix well.

Gradually add the flour mixture to the butter mixture and beat on medium speed until just combined.

Scoop 1.5 tablespoon sized balls of dough onto the cookie sheets, 2 inches apart.

Bake for 9-11 minutes, or until golden brown around the edges with no uncooked centers.

Remove cookies from the oven and transfer to a wire rack to cool.

To make the icing, combine all the icing ingredients except for the powdered sugar in a small saucepan.

Heat on low until sugar is melted, then turn heat to medium to bring to a boil.

Boil for 3 minutes, stirring occasionally, then remove from heat and immediately pour into a heat-proof glass bowl.

Whisk in the powdered sugar and allow to cool and thicken, roughly 10-15 minutes. If you find your icing to be a little thick, just add a touch more water to thin it back out. If it’s too thin, add a little more powdered sugar.

Spread the icing onto the cookies and then allow to cool. The icing will thicken as it cools.