Hazelnut Jam Thumbprints

Directions

1. 1
   Put butter and 1/2 cup sugar in the bowl of an electric mixer fitted with the paddle attachment; mix on medium speed until pale and fluffy, about 3 minutes.
2. 2
   Add egg yolk and vanilla, and mix well.
3. 3
   Reduce speed to low.
4. 4
   Add flour and salt, and mix until just combined.
5. 5
   Refrigerate dough for 2 hours.
6. 6
   Preheat oven to 325F.
7. 7
   Stir together hazelnuts and remaining 2 tablespoons sugar in a small bowl.
8. 8
   Roll dough into 1-inch balls; dip balls in beaten egg white, then in hazelnut mixture.
9. 9
   Space 1 inch apart on baking sheets lined with parchment paper.
10. 10
    Press down center of each ball with your thumb.
11. 11
    Bake for 10 minutes.
12. 12
    Remove from oven; press down centers again with the lightly floured end of a wooden spoon.
13. 13
    Return to oven.
14. 14
    Bake cookies until golden brown, 8 to 10 minutes more.
15. 15
    Let cool slightly on sheets on wire racks.
16. 16
    Fill each center with jam.
17. 17
    Cookies can be stored in a single layer in airtight containers at room temperature up to 2 days.