Whisk together flour and baking powder in a bowl; set aside. Pulse pecans, confectioners’ sugar, salt, and cinnamon in a food processor until finely ground (but not wet); transfer to the bowl of an electric mixer fitted with the paddle attachment.

Add butter and granulated sugar to the mixer bowl; beat on medium speed until fluffy. Mix in vanilla and egg, then reduce speed to low. Add flour mixture and continue mixing on low until combined. Halve dough, shape into disks and wrap in plastic. Refrigerate until firm, at least 2 hours.

Heat oven to 375º. Line two baking sheets with parchment paper or a nonstick baking mat. Working with 1 disk at a time, roll out dough on a lightly floured surface to ⅛-inch thick. Use a 2-inch fluted cutter to cut out shapes. Cut out centers of half the rounds with a ½-inch heart cutter; re-roll scraps. Space cookies 2 inches apart on baking sheets. Chill dough on baking sheets for 5 minutes.

Bake cookies and hearts until pale golden, 8 to 10 minutes. Transfer to racks to cool. Snack on tiny heart cookies while waiting.

Dust the tops (the cookies with cutouts) with confectioners’ sugar. Spread jam or Nutella onto the bottoms; then sandwich with sugared tops. Store in an airtight container up to 2 days.