I love tart lemon desserts. This is a recipe I found on Betty Crocker that looks very good.
Ingredients:
Cookies

* 1 cup butter or margarine, softened
* 1/3 cup powdered sugar
* 1 teaspoon vanilla
* 1 2/3 cups flour
* 1 tablespoon powdered sugar

Filling

* 2/3 cup granulated sugar
* 3 teaspoons lemon peel, grated
* 3 tablespoons lemon juice
* 1 tablespoon butter or margarine
* 1 teaspoon cornstarch
* 1/4 teaspoon salt
* 1 egg, beaten

Directions
In large bowl, Beat butter, 1/3 C powdered sugar, and vanilla with mixer on medium speed until well blended.

*Stir in flour until dough forms.
*Cover; refrigerate 30 minutes
*Heat oven to 350°F Shape dough into 1" balls.
*Place balls 2" apart. Press thumb into center of each ball to make indentation.
*Bake 8 to 10 minutes or until golden brown.
*Remove to cooling racks and cool completely, about 30 minutes.
*In 1 qt saucepan, heat all filling ingredients over low heat about 25 minutes, stirring constantly, until smooth and thickened.
*Cool about 15 minutes.
*Fill each thumbprint with rounded 1/4 tsp filling. Sprinkle 1 T powdered sugar over cookies.