Put oven rack in middle position and preheat oven to 350°. Toast hazelnuts in shallow baking pan until fragrant and skins begin to loosen, about 6 minutes. Rub nuts in kitchen towel to remove any loose skins (some skins may not come off); cool to room temperature.
Pulse nuts and 1/4 cup brown sugar in food processor until nuts are finely ground. Whisk together flour, baking powder, salt and cinnamon in small bowl. Beat together butter and remaining 1/4 cup brown sugar in large bowl with electric mixer at medium-high speed until pale and fluffy, about 3 minutes in stand mixer (preferably fitted with paddle) or 6 minutes with handheld. Add nut mixture and beat until combined well, about 1 minute. Beat in egg and vanilla. Reduce speed to low and add flour mixture; mix until just combined.
With floured hands, form dough into 2 balls and flatten each into 5-inch disk. Chill disks, wrapped in plastic wrap, until firm, at least 2 hours.
Put oven racks in upper and lower thirds of oven and preheat to 350°. Roll out 1 disk of dough into 11-inch round (1/8-inch thick) between 2 sheets of wax paper (keep remaining dough chilled). If dough becomes too soft to roll out, rewrap in plastic and chill until firm. Cut out as many cookies as possible from dough with larger cookie cutter and transfer to 2 ungreased large baking sheets, arranging about 1 inch apart. Using smaller cutters, cut out centers from half the cookies, reserving centers and rerolling along with scraps (reroll only once).
Bake cookies, switching position of sheets halfway through baking, until edges are golden, 10 to 15 minutes total; transfer to racks to cool completely. Make more cookies from second disk.
Spread about 1 teaspoon jam on flat side of 1 solid cookie and sandwich jam with flat side of windowed cookie. Sandwich remaining cookies in same manner.
Note: Cookies keep, layered between sheets of wax paper or parchment, chilled in airtight container 2 weeks.
The key to delicious Linzer cookies is striking just the right balance of the tart raspberry jam filling with the thin, tender and slightly sweet cookies. These only get better after a few days.