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1
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter, sugar, vanilla, and salt on medium speed until light and fluffy, about 5 minutes.
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2
Gradually add the eggs, scraping down the bowl after each addition. Reduce the speed to low.
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3
Sift the flour, cinnamon, cake crumbs, and baking powder together into a medium bowl. Add to the creamed mixture all at once and mix just until incorporated. Scrape down the bowl as needed.
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4
Add the hazelnut flour and mix just until combined. Divide the dough into two equal pieces, wrap in plastic wrap, and refrigerate until chilled, about 15 minutes.
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5
While the dough is chilling, preheat the oven to 350 degrees F. Line two baking sheets with parchment paper.
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6
On a lightly floured surface, roll out the chilled dough to about 1/4 inch thick. Cut rounds of dough using a fluted circular cookie cutter. Use a smaller cutter to cut a hole in half of the rounds. Transfer the cookies to the prepared baking sheets, spacing them about 1 1/2 inches apart. As you are working, reserve the scraps so that they may be rolled again and cut.
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7
Bake until lightly golden brown, 8 to 10 minutes.
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8
Allow the cookies to cool for a minute on the baking sheets then transfer, using a spatula, to a cooling rack and allow to cool completely.
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9
Sift confectioners' sugar over the cooled cookies. Coat the cookies without holes lightly and the ones with holes thoroughly. Pipe or spread a thin layer of jam on the cookies without holes. Top with the remaining cookies and press gently to secure.
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10
Store the cookies in an airtight container.
