1Preheat oven to 375 degrees. Lightly grease cookie sheet, set aside. Beat butter, sugar, and 1/8 tsp salt on med speed until combined. Beat in as much flour as you can with mixer. Stir in remaining flour and the hazelnuts. Gently knead dough in bowl until it holds together. Divide dough in half, form each half into a ball.
2On lightly floured surface, roll a dough ball until 1/4" thick. Cut out with a 2"-3" star cookie cutter. Repeat with remaining dough. Using a 1" star cookie cutter, cut out the center of HALF the star cutouts.
3Place cutouts 2" apart on prepared cookie sheet. Bake 6-8 mins or until edges are very lightly browned. Transfer to wire rack and cool.
4Spread each of the large whole stars with jam. Gently place a "windowed" cookie on top and sprinkle with powdered sugar. Store in refrigerator. You may also store unfilled cookies at room temperature for up to 3 days, or freeze for up to 3 months. Thaw if frozen and fill with jam when ready to serve.