1. Using an electric mixer on medium-high speed, beat butter until light, 2 minutes. Beat in 2/3 cup sugar and zest, then egg and salt. Beat in flour 1 cup at a time. Divide dough in half and form into 2 disks. Wrap in plastic wrap and chill for at least 1 hour or overnight.
2. Preheat oven to 375ºF; line 2 large baking sheets with parchment. On a lightly floured surface, roll out a disk to 1/4-inch thickness. Cut out cookies with a 2 1/2-inch cutter. Place 1/2 inch apart on sheets. Gather dough scraps, reroll and cut more cookies. Sprinkle cookies with 1 1/2 tsp. sugar. Repeat with remaining dough disk.
3. Bake cookies until golden around edges, 10 to 12 minutes. Place baking sheets on wire racks for 5 minutes, then transfer cookies to racks to cool.
4. Spread 1 tsp. jam on bottom of a cookie; sandwich with another. Repeat with remaining cookies and jam.
Bake time is per batch.