Preheat oven to 300°; lightly grease two 9-inch round cake pans; sprinkle each pan with 1 tablespoon of the maple sugar.
In a bowl, cream together the butter, salt, regular sugar, ½ cup maple sugar, maple extract, and vanilla; then beat in the flour.
Divide the dough in half and press it into the prepared pans, smoothing surface with your fingers.
Sprinkle each round with 1 tablespoon of the remaining maple sugar, pressing it in gently.
Prick the dough with a fork in an attractive pattern.
Bake for 35-40 minutes, until it is golden brown around the edges.
Remove it from the oven and loosen the edges with a heat-resistant plastic knife or table knife.
Wait 5 minutes, then carefully turn the shortbread out onto a clean work surface, all in one piece.
Using a pizza wheel or sharp knife, cut each round into 12 wedges (do this while the shortbread is still warm; if you wait until it is cool, it will not cut easily).
Transfer the wedges to a rack to cool.