In a large mixing bowl combine the cream cheese, butter, and granulated sugar.
Add the salt, baking powder, vanilla extract, lemon extract, and egg yolk and combine.
Add the flour and combine.
Using approximately 2 tablespoon worth of dough, shape the dough into round balls. Place on a baking sheet.
Bake for 10 minutes.
Upon removing the cookies from the oven create an indentation in the middle of each of the round cookies. If you have a round 1 teaspoon measuring spoon, use the back of this to make the indention. Otherwise, the rounded end of a cooking tool, like a whisk will do the trick. Allow to cool fully before moving to a drying rack to prevent misshapen cookies.
Lemon Curd
In a medium bowl whisk the egg yolks.
In a separate medium saucepan, whisk together the lemon zest, lemon juice, sugar, and salt. Place on medium heat and bring to a simmer.
While whisking the egg yolks constantly, add the simmering lemon juice mixture to the egg yolks. Then add the egg yolk mixture back into the saucepan and return to medium heat, whisking constantly for 3-5 minutes or as much as 10 minutes until thickened. Whisk constantly to prevent the eggs from scrambling.Keep in mind that stovetop temperatures can vary for any given temperature setting. The actual temperature and resulting impact on the food depend on the stove that you are using (gas vs electric), stovetop brand, size of the burner, surface area, thickness of the saucepan, etc. You may need to adjust the cooking time based on your kitchen setup.
To create a smooth curd, strain the mixture through a fine mesh strainer.
Assembling the Cookies
Place the cooled lemon curd in a piping bag (or a gallon bag with the tip cut off) and fill the indentations of each cookie with lemon curd. You can also do this with two small spoons.
Keep the cookies in a single layer (don’t stack on them top of each other) to prevent the lemon curd in the cookies from getting smashed.
Store any leftover cookies in the refrigerator.
Notes
Softening Butter: If you have not already softened your butter add the butter to your mixing bowl and microwave for 1 minute at 20 percent power. Flip the butter over and add another minute at 20 percent power. The same is true for the cream cheese.Oven Temperature: These cookies are baked at 325℉, which is slightly lower than the more typical 350℉. This helps to create an extra gooey soft cookie and prevents browning.Creating the Indentation: Create the indentation in the cookie while the cookies are still warm. This will help the cookies to hold the indented shape.If you make the indentation before the cookies are baked, the indentation will change shape as the cookies bake in the oven and you will not get a nice round indentation in the center.Cooling the Cookies: Do not move the cookies off the baking sheet until they have fully cooled. They are very soft cookies and moving them too quickly will cause them to become misshapen.After Removing The Curd From The Stove: Do not let the curd sit in the hot saucepan after removing it from the heat on the stove. If you do the heat could scramble the eggs.