Preheat the oven to 375 degrees. Place hazelnuts on a baking sheet, and toast in the oven for 10 minutes. Remove from oven, and immediately transfer nuts to a clean towel. Vigorously rub the nuts in the towel to remove as much of the skins as possible. Set nuts aside until completely cool. Place nuts in a food processor, and process until finely ground. Set aside.
In the bowl of an electric mixer fitted with the paddle attachment, beat butter and sugar on medium speed until light and fluffy, about 2 minutes. Add egg, and beat until smooth, about 3 minutes. Beat in vanilla.
Whisk together reserved hazelnuts, flour, baking powder, cinnamon, nutmeg, and salt. Add to butter mixture; beat on low until combined, about 2 minutes. Form dough into two flattened disks, wrap each with plastic wrap, and refrigerate until firm, at least 1 hour or overnight.
Preheat oven to 350 degrees. Have ready two baking sheets lined with Silpats (French baking mats; see sources) or parchment paper. Also have ready one 2 1/2-inch round fluted cookie cutter and one 3/4-inch cookie cutter. On a lightly floured work surface, roll out half the dough to a scant 1/4-inch thickness. Using the 3-inch fluted cutter, cut out cookies. With a wide spatula, transfer cookies to the prepared baking sheets. Using the smaller cutter, cut the centers out of half of the cookies. Repeat rolling and cutting with the other half of the dough. Combine the scraps from both batches, reroll and cut.
Bake until the edges are golden, 12 to 16 minutes, rotating halfway through. Remove from oven; place on wire racks until completely cool.
Lightly sift confectioners' sugar over the decorative tops; set aside. Spread a scant tablespoon of jam on the bottoms of each cookie, and sandwich with the sugar-dusted tops.