Preheat the oven to 350°F (177°C). Line two large baking sheets with parchment paper or silicone baking mats and set aside.

In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl using a handheld mixer, beat the butter until smooth. Add the granulated sugar and lemon zest and continue mixing for 1 to 2 minutes or until well combined.

Mix in the egg yolks, lemon extract, and salt until fully combined.

Add the flour and mix until fully combined. The mixture will be a little crumbly at first, but it will come together as you continue mixing it.

Using a one-tablespoon cookie scoop or measuring tablespoon, measure out the cookie dough, roll in granulated sugar (optional), then place onto the prepared baking sheets.

Using the bottom of a ½ teaspoon measuring spoon, gently press an indentation into the center of each ball of cookie dough.

Spoon ½ teaspoon of lemon curd into the indentation of each one.

Bake for 12 to 14 minutes or until the cookies are set and the bottoms are lightly browned.

Remove from the oven and cool on the baking sheets for 10 minutes, then carefully transfer the cookies to a wire rack to cool completely.