In a standing electric mixer cream together butter and sugar until light and fluffy and beat in maple syrup and egg yolk until mixture is combined well. Sift together salt and flour over mixture and fold in thoroughly. Chill dough, wrapped in plastic wrap, until firm, about 2 hours. Dough may be made 4 days ahead and chilled.

Preheat oven to 350°F.

Divide dough in half. Keeping one half chilled, lightly flour other half and on a lightly floured surface gently pound with a rolling pin to soften. Roll out dough 1/8 inch thick and with a 3-inch floured maple-leaf cookie cutter cut out cookies, chilling scraps. Arrange cookies on buttered baking sheets and if desired, with back of a knife, mark cookies decoratively. Make more cookies in same manner with remaining dough and with all the scraps pressed together.

Bake cookies in batches in middle of oven until edges are golden, about 12 minutes, and transfer to racks to cool. Cookies keep in airtight containers 1 week.

Makes about 40 cookies.