Key Lime Thumbprints

From Martha Stewart Living.

• Ready In: 1 hr 15 mins
• Serves: 60
• Yields: 60 cookies

Ingredients

• For the Dough

• 1  cup unsalted butter, softened
• 1⁄2 cup sugar
• 2  large  egg yolks, room temperature
• 1  teaspoon vanilla extract
• 2 1⁄2 cups all-purpose flour
• 1  teaspoon coarse salt

• For the filling

• 1  cup sugar
• 3  tablespoons all-purpose flour
• 3  large eggs, room temperature
• 1  tablespoon key lime zest, finely grated
• 3  tablespoons  fresh key lime juice
• 1⁄4 teaspoon coarse salt
•  confectioners' sugar, for dusting

Directions

1. Make the Dough: Cream butter and sugar with a mixer until pale and fluffy. Add yolks and vanilla, and beat for 1 minute. Reduce speed to low, and beat in flour and salt until combined. Cover, and refrigerate until firm, about 1 hour (or up to 1 day).
2. Preheat oven to 325 degrees.
3. Make the Filling: Whisk sugar, flour and eggs in a medium bowl. Stir in lime zest, juice and salt.
4. Roll balls of dough using 2 teaspoons dough for each. Place 1 inch apart on parchment lined baking sheets. With the handle of a wooden spoon, press gently in the center of each to creat an indentation.
5. Bake for 10 minutes. Press centers if indentation loses definition.
6. Spoon filling into centers. Bake until cookies are light brown around edges, 6-8 minutes.
7. Let cool on wire racks.
8. Cookies will keep, covered, for up to 2 days.
9. Just before serving dust with confectioner's sugar.