Melt the butter over medium-low heat, pour it into a mixing bowl, and add the egg and sugar. Mix until well combined. You may also mix it in a stand mixer (KitchenAid) at low speed;
Then add the 3 types of flour and process well;
Add the lemon zest, vanilla extract, and salt. Mix until it’s a thick, wet consistency (just not liquid). This is a very important part of the process. If the mixture has too much liquid, the cookies will lose their shape. If it is too thick, it can’t be put into a piping bag and will be too crumbly;
Put the dough into a piping bag with a Wilton 1M (15mm) star-shaped piping tip.
Pipe rings about 2-inches in diameter (5-6cm) onto a baking tray lined with parchment paper. Allow enough space as they will expand.
Bake in a static oven at 350°F (180°C) for 15 - 20 minutes until light golden.