In a medium bowl, whisk together flour, baking powder and salt; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugars until light and fluffy, about 3 minutes. Add the egg and maple extract; beat at medium speed until combined, about 30 seconds. Add the dry ingredients and beat at low speed until just combined, about 30 seconds, scraping down the bowl as needed.
Divide dough into two balls and flatten each ball into a disk. Wrap each disk in plastic wrap and refrigerate at least 1 hour.
Preheat oven to 375 degrees F. Line baking sheets with parchment paper. Remove dough from refrigerator onto a lightly floured surface.
With a rolling pin, roll the dough out to 1/4-inch thickness. Use a maple leaf cookie cutter to cut out cookies, placing on prepared baking sheet.
Bake cookies in preheated oven 8-10 minutes, or until edges just start to brown.
Cool the cookies on the baking sheets about 3 minutes; using a wide metal spatula, transfer the cookies to a wire rack and cool to room temperature.
While cookies are cooling, make the filling by creaming butter in a stand mixer. Add confectioners sugar and maple syrup and beat until combined and smooth.
Using a knife or spoon, spread the filling onto the backside side of the cookie. Top with another cookie, backside down. Repeat with the remaining cookies.
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