Whirl 3/4 cup sesame seeds in a food processor until finely ground. Add flour, sugar and salt. Pulse until combined. Add butter and vanilla through the feed tube while pulsing until dough comes together.
Scoop 1 tbsp of dough and roll into a ball. Lightly dip tip of ball into remaining sesame seeds. Place on baking sheet, seed-side up, and gently flatten to 1/2-in.- thick disc. Repeat with remaining dough and seeds.
Bake in centre of oven until edges of cookies are just starting to brown, 9 to 11 min. Let cookies cool on sheet for 1 min. Transfer to a rack to cool completely. Store in an airtight container up to 1 week or freeze up to 1 month.