Preheat oven to 350°F.
In your mixer, beat together the butter, powdered sugar, and lemon juice. It'll look a little chunky; that's fine.
Sift in the flour and keep mixing for 2-4 minutes. You're looking for a texture like sand, which will then incorporate into a dough.
Take this dough ball and roll it out flat, to about 1cm thick. The cookies don't rise or spread out when baking, so pick the shape you want them to be.
Use a cookie cutter to cut out your cookies. Take excess, re-ball and re-roll, and repeat until all dough has been cut. Arrange them on your baking sheet and baking mat.
Bake for 6-7 minutes. They won't brown, so be careful. If you made your cookies a little thin, it won't take quite as long to bake.
Pull the cookies out and let rest for a minute. Then, carefully transfer them to a cooling rack. While they cool, make your icing.
To make the icing, mix the icing ingredients. Adjust the liquid and sugar to reach the consistency you want.
Spread the icing over your cookies. I use a spoon, but you can pipe it too. Decorate with colored icing or even sprinkles, or just leave it plain. That's it!