Preheat the oven to 350°F for 10 minutes and line a baking sheet with parchment paper.
Cut butter into cubes. Then, cream together the vanilla, salt, lemon zest, granulated sugar, and butter in a large bowl. Mix together with a hand mixer or an electric mixer until all the ingredients are well integrated.
Add the lemon juice and egg yolk and keep mixing for another two minutes or until they integrate.
In another bowl, combine the remaining dry ingredients: baking powder, cornstarch, and flour until they are fully integrated.
Combine the dry mixture with the wet butter mixture and integrate both until a smooth dough forms. You can do this step using your hands or a spatula. Now take the dough to the fridge for about 1 hour. Don’t skip this step as it will make it easier to scoop later.
Scoop 1 heaping teaspoon of dough and shape it into a ball (it will spread a bit on the oven), then place it on the baking sheet and do the same with the rest of the dough. Leave 2 inches between each ball.
Bake for about 10-12 minutes or until they start to get brown on the edges. We don’t want them to look golden brown but they don’t have to look raw either. Just a little puffy on the center.
Let the cookies sit on a cooling rack. Then toss each cookie in powdered sugar. Serve and enjoy!
Notes
Use room temperature ingredients. Bringing eggs and butter to room temperature will ensure that the dough mixes evenly! Take the butter out at least an hour before you're about to make the dough. If you forget, no worries! Microwave some water in a glass, dump the water out and then place the glass upside down over the stick of butter. This will help soften the butter!
Don’t overmix the dough. Over-mixing develops the gluten in the flour, which can result in dry cookies!
Chill the dough! Chilling the dough will ensure that cookies don't spread out too much. After making cookie dough, cover with plastic wrap and chill in the fridge for a few hours, if you can
Don't over-bake the cookies. Make sure to take them out of the oven while they're still nice and soft in the center. They may look slightly underdone but trust me, they'll continue to bake as they cool on the baking sheet!
Let them cool completely before dusting them with powdered sugar.