To make the lemon curd, add the lemon juice, lemon zest, egg yolks, granulated white sugar and salt to a small saucepan or pot. Whisk everything together.

Heat the lemon mixture over medium low heat for 20-25 minutes, stirring frequently, until thick. It should coat the back of a spoon once thick enough.

Remove it from the heat and slowly whisk in the cold, cubbed butter.

Once all of the butter is melted in, transfer the curd to a heat proof, medium bowl. Place plastic wrap on top of the curd, so it doesn't form a skin, and allow it to cool completely.

In a small bowl, whisk together the flour, baking powder and 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.)

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.

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 tbsp portions and roll them into balls. After each ball is rolled, immediately press it with a ½ tsp 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 tsp 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!