Heat oven to 375 degrees F.
Toast hazelnuts until skins darken and begin to split, about 15 minutes. Transfer to a clean dish towel, and rub vigorously to remove skins; discard skins. Place nuts in a food processor; pulse until medium fine.
Line 2 baking sheets with parchment paper; set aside. In the bowl of an electric mixer, beat butter and granulated sugar at medium-high speed until light and creamy, about 2 minutes. Add eggs; beat until smooth, about 3 minutes. Beat in vanilla.
In a large bowl, combine flour, hazelnuts, baking powder, cinnamon, salt, and zest. Add to butter mixture; beat to combine, about 1 minute. Place in freezer until very firm, about 30 minutes.
Liberally dust a clean surface with flour, and roll out dough to 1/8-inch thickness. Using a 3-inch heart-shaped cookie cutter, cut out 72 hearts. To make top halves of cookies, use a 1-inch heart-shaped cookie cutter to cut out centers from 36 of the hearts.
Transfer cookies to prepared baking sheets, and bake until golden brown, about 8 minutes. Transfer to a wire rack until completely cooled.
Lightly sift confectioners' sugar over cookie tops. Spread about 1 teaspoon jam on each of the bottom halves, and sandwich both halves together. Store in an airtight container for up to 1 week.
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