In a small bowl, whisk together the egg yolks, key lime zest, key lime juice, sugar and salt. Transfer to a small saucepan.

Cook the mixture over low-medium heat, stirring constantly, until it is thick enough to coat the back of a spoon, 3 to 5 minutes.

Remove from heat and add the butter. Mix until smooth.

Transfer the curd to a small bowl and cover with plastic wrap.

Refrigerate until chilled, about 30 minutes.

Combine all ingredients in a large bowl and mix well.

Drop by tablespoonfuls (I used a cookie scoop) onto baking sheets lined with parchment paper or silicone baking mats.

Using the end of a wooden spoon or your finger, make a small indentation on top of each mound.

Bake at 300 degrees for 20-25 minutes, or until the cookies are pale golden brown on the edges.

Cool for 2 minutes on the baking sheets, then transfer to a wire rack to cool completely.

Once the cookies are cool, fill the centers of each with about 1 tsp. key lime curd.