A double dose of maple sets these leaf-shaped sandwich cookies apart: maple sugar goes into the buttery shortbread dough, and maple syrup sweetens the rich cream filling.
In a medium bowl, whisk together flour, baking powder, cinnamon, and salt; set aside.
In the bowl of an electric mixer fitted with the paddle attachment, cream together butter and sugars on medium speed until light and fluffy, about 3 minutes. Add eggs and beat until combined, about 30 seconds. Add flour mixture and beat on low speed until just combined, about 30 seconds, scraping down sides as necessary.
Divide dough into four disks; wrap each in plastic and refrigerate at least 1 hour.
Preheat oven to 375 degrees. On a lightly floured surface, roll out one disk of dough 1/8 inch thick, lightly dusting with flour to prevent sticking. Cut out cookies using a 4-inch maple-leaf-shaped cutter, dipping cutter in flour as needed. Transfer to parchment-lined baking sheets and freeze until firm, about 10 minutes. Repeat process with remaining dough.
Bake, rotating halfway through, until edges begin to brown, 10 to 12 minutes. Let cool on sheets 3 minutes, then transfer to a wire rack to cool completely.
In the bowl of a electric mixer fitted with the paddle attachment, cream butter until light and fluffy. Add confectioners' sugar and maple syrup; beat until smooth. Transfer to a piping bag fitted with a small round tip. Pipe 2 tablespoons filling onto bottoms of half the cookies, then sandwich with remaining cookies. Filled cookies can be stored in an airtight container at room temperature up to 3 days.
When cutting out cookies, cut out half of the cookies, then flip cutter over and cut out remaining cookies to get identical leaves for making sandwiches.