In a small bowl, whisk together the flour, baking powder and salt.
2 ½ cups (313 g) all-purpose flour, spooned and leveled, ½ teaspoon baking powder, ½ teaspoon sea salt
In a large bowl, cream butter and granulated white sugar together with and electric mixer on high speed until it's fluffy, about 2-3 minutes. (If using a stand mixer, use the paddle attachment.)
1 cup (224 g) unsalted butter, softened, 1 cup (200 g) granulated white sugar
Add in the egg yolk, vanilla and lemon zest and mix on medium-high speed until pale in color and fluffy, about 1-2 minutes.
1 egg yolk, 1 teaspoon (5 ml) vanilla, 1 teaspoon (3 g) lemon zest
Add in the dry ingredients and mix on low then medium speed just until combined. (Scrape the sides of the bowl as necessary.)
Scoop the dough into 1 tablespoon portions and roll them into balls. After each ball is rolled, immediately press it with a ½ teaspoon to make an indent.
Chill the prepared cookie dough balls on parchment paper lined baking sheets for 1 hour.
Preheat the oven to 350 degrees.
Once chilled, separate the cookies 12 at a time on a prepared, parchment paper lined baking sheet.
Bake the cookies for 9-10 minutes.
When the cookies are straight out of the oven, scoot a small, round cookie cutter around them in a circular motion to help them return to their original smaller sizer. You can also press the centers again with a ½ teaspoon to create a deeper indent.
Let the cookies cool for 5 minutes on the cookie sheet, then transfer them to a cooling rack to completely cool.
Once the cookies are completely cooled, spoon about 1 teaspoon of lemon curd into the center of each cookie. (If you desire, you can sprinkle powdered sugar over the cookies before adding the lemon curd filling.)
Then serve!