Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
Cream together butter, tahini, and sugar until smooth.
Add egg and vanilla extract, mixing until fully incorporated.
Whisk together flour and baking soda, then gradually fold into the wet mixture.
Scoop dough onto the baking sheet, flattening slightly with a fork or spoon.
Sprinkle sesame seeds on top if desired.
Bake for 10–12 minutes until lightly golden around the edges.
Cool on the baking sheet for 5 minutes before transferring to a wire rack.