Place the nuts and brown sugar in a food processor. Pulse into a very fine crumb. Set aside.

In a medium bowl, whisk together the flour, baking powder, cinnamon, and salt. Set aside.

In a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter and granulated sugar together on medium-high speed until completely smooth and creamy, about 3 minutes. Add the egg and vanilla extract, and beat on high speed until combined, about 1 minute. Scrape down the sides and bottom of the bowl and beat again as needed to combine.

Add the flour mixture and the ground nut mixture to the wet ingredients and mix on low speed until combined. It will be crumbly at first, but will come together after a couple minutes of mixing.

Divide the dough into 2 equal portions, gently flatten into discs, and wrap each in plastic wrap. Chill the discs in the refrigerator for at least 3 hours and up to 4 days.

Preheat the oven to 350°F (180°C). Line large baking sheets with parchment paper or silicone baking mats. Set aside. If the dough chilled for longer than 3 hours, allow to sit at room temperature for at least 20 minutes before rolling because the dough will be quite hard.

Generously flour a work surface, as well as your hands and rolling pin. Roll out the first disc of dough to ¼-inch thickness. Using a 2-inch round or fluted cookie cutter, cut the dough into circles. Re-roll the dough scraps and continue cutting until all is used. Repeat with the second disc of dough. You should have about 64 circles.

Using a 1-inch round or fluted cookie cutter, cut a hole into the center of 32 of the circles. Arrange the whole circles and the donut cookies 2 inches apart and on separate baking sheets.

Bake the whole circles for about 11 minutes, or until lightly browned around the edges, and bake the donut cookies for about 10 minutes. Allow cookies to cool on the baking sheets for 5 minutes. Dust the donut cookies with confectioners’ sugar, then transfer all of the cookies to a cooling rack to cool completely before assembling.

Spread ½ teaspoon of jam on the bottom of each whole cookie. Carefully top each with a donut cookie and press down gently to create a cookie sandwich.

Store tightly covered at room temperature for up to 3 days or in the refrigerator for up to 1 week.