On waxed paper, mix flour and salt.

In a large bowl, with mixer on medium speed, beat butter and sugars until just blended and creamy, occasionally scraping bowl with a rubber spatula. Add syrup and vanilla; beat until mixed. Reduce speed to low; gradually beat in flour, then pecans, just until blended, scraping bowl.

Divide dough into 2 equal pieces. Flatten each piece into a disk and wrap each in plastic wrap. Refrigerate at least 1 hour or up to 3 days. Let stand until pliable enough to roll.

Preheat oven to 350 degrees F. Line cookie sheets with parchment paper.

Between sheets of waxed paper, roll 1 disk of dough 1/4 in. thick. Remove the top sheet of waxed paper. With 2- to 4-in. leaf-shaped cutters, cut dough into as many cookies as possible. Refrigerate trimmings. Place cookies, 1 inch apart, on prepared sheets.

Bake cookies 12 to 15 minutes or until golden brown. Transfer cookies to wire rack to cool. Repeat with remaining dough and trimmings.

When cookies are cool, brush with syrup to glaze, if desired. Sprinkle sanding sugar over syrup glaze, if desired. Let sugared cookies dry 1 hour.

Store cookies (with waxed paper between layers if decorated) in airtight containers at room temperature up to 1 week, or in the freezer and up to 3 months.