- With the rack in the middle position, preheat the oven to 180 °C (350 °F). Line a baking sheet with parchment paper.
- In a bowl, with an electric mixer, cream the butter and maple sugar for about 2 minutes. Add the maple syrup and beat until smooth.
- In another bowl, combine the flour and baking powder. With a wooden spoon, combine with the previous mixture until the dough is smooth. Divide the dough into four pieces. Cover with plastic wrap and refrigerate the unused dough when preparing the cookies.
- Roll out the dough, one piece at a time, on a floured work surface to a thickness of 0.3-cm (1/8-inch). Cut out cookies with a 5.6-cm (2 ¼-inch) maple leaf cookie cutter (you can also use a glass or other cookie cutter). With a knife, cut grooves on each cookie to mimic leaf veins. Place the cookies on the baking sheet as you go. If desired, brush with milk and sprinkle with coarse maple sugar.
- Bake in the oven for 8 to 10 minutes or until cookies are lightly browned. Let cool.
- In a bowl, beat all the ingredients together until smooth. Set aside.
- Generously spread maple filling on half the cookies and cover with the remaining cookies.