From the blog For Love of the Table
1 3/4 c. all-purpose flour (200 grams)
a scant 2/3 cup hazelnuts (83 grams), toasted, peeled and ground to a flour (see notes)
1 t. cinnamon
1/2 t. salt
1/2 lb. unsalted butter, softened
1/2 c. granulated sugar
2 eggs, separated
1 1/2 t. vanilla
zest of 1 lemon (optional)
3/4 c. hazelnuts, toasted, peeled and ground medium fine
2/3 to 3/4 c. best-quality seedless raspberry jam, well-stirred
Place the flour, finely ground hazelnuts, cinnamon and salt in a medium bowl and whisk to combine. Set aside.
Briefly cream the butter and sugar. Beat in the egg yolks, vanilla and zest (if using). Add the dry ingredients and stir just until well incorporated. Scrape the dough onto a piece of plastic wrap, press into a thick disc and refrigerate for about 2 hours or until the dough is firm.
When ready to bake the cookies, place the egg whites in a small bowl and beat until foamy. Place the ground hazelnuts in a wide shallow dish (a pie plate works well). Divide the jam between 2 small zip-lock bags.
Divide the dough into 6 equal portions. Work with one section at a time. Knead the dough between lightly floured hands until malleable. Roll into a 10-inch sausage and then cut into 10 1-inch segments. Repeat with 2 more sections of dough so that you have 30 segments (enough to fill one cookie sheet). Roll the segments into balls. Dip the balls into the egg white and then roll them in the hazelnuts. Place the hazelnut coated balls of dough onto a parchment lined baking sheet, spacing evenly (about 1 1/2 inches apart). Using the end of a round handled wooden spoon or rubber spatula (something about 1/2- to 5/8-inch in diameter), create a depression in the center of each ball—pressing deeply, but not all the way through and being careful not to crack the edges of the cookie (if the dough cracks, carefully press back together). You will need to occasionally flour the end of the wooden spoon as you work to keep it from sticking.
Place the baking sheet in the center of a preheated 350° oven and bake for 10 minutes. Remove the sheet from the oven and using the same implement you used to make the depressions, press the middle of the cookies back down. Cut a corner off of the zip-lock bag (don't make the hole too big) and carefully pipe a small amount of jam into each depression. The jam should barely come up to the edges of the depression in the cookies. Return the cookies to the oven and bake until they are golden and the jam is bubbling in the center of the cookie—another 5 to 10 minutes. Cool the cookies on the sheet for 5 minutes. Carefully transfer the cookies to wire racks and cool completely. Repeat with the final three sections of dough.
If you like, lightly dredge the cookies with powdered sugar. Store in an air tight container. Makes 5 dozen cookies.
Notes:
The lemon zest is a traditional component of "Linzer" dough. I prefer these cookies without it—but they are delicious either way.
If you don't have a nut grinder, you may purchase hazelnut flour. Or, prepare the dough in the food processor: Process the toasted, skinned hazelnuts and the sugar until the nuts are ground very finely. Cut the butter into a few pieces and add. Process until smooth and creamy. Process in the egg yolks, vanilla and zest (if using) just until incorporated. Scrape the sides of the bowl and add the dry ingredients. Pulse just until the flour is incorporated.
http://www.forloveofthetable.com/2012/12/linzer-thumbprint-cookies.html