1. Preheat oven to 325°. Cook sesame seeds in a heavy skillet over medium heat, stirring often, 6 to 7 minutes or until browned and fragrant. (Seeds will be the color of pecans.) Transfer to a plate. Cool completely (about 20 minutes).
2. Process flour, next 2 ingredients, and 1 Tbsp. seeds in a food processor 30 seconds or until seeds are finely ground. (Seeds should be the same consistency as flour.) Add butter, and pulse 5 or 6 times or until mixture resembles small peas and is crumbly. Add half of ice-cold water, 1 Tbsp. at a time, and pulse 2 or 3 times or just until combined. Add 1 Tbsp. sesame seeds and remaining water; process 10 to 15 seconds or until dough forms a ball and pulls away from sides of bowl.
3. Place dough on a lightly floured surface. Shape into a 1 1/2-inch-thick flat disk; cut into 4 wedges.
4. Dust top of 1 dough wedge with flour; roll dough to 1/16-inch thickness on a lightly floured surface. Sprinkle with 2 tsp. sesame seeds; roll gently to press seeds into dough. Cut dough with a 2-inch round cutter. Place wafers 1/2 inch apart on parchment paper-lined baking sheets. Repeat procedure with remaining dough wedges and sesame seeds.
5. Bake at 325° for 23 to 25 minutes or until lightly browned. Cool completely on baking sheets on wire racks (about 20 minutes). Store in an airtight container up to 3 days.