In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugars until light a fluffy, about 3-5 minutes. Add tahini and vanilla and mix until combined
In a separate bowl, whisk flour, baking powder, and salt. Add to butter mixture and mix on low speed until there are no more dry spots. Transfer the dough to a piece of plastic wrap and cover tightly. Refrigerate 30 minutes.
Preheat oven to 350 degrees F. Line 2 baking sheets with parchment paper.
Roll out chilled dough between two sheets of parchment paper, to ¼-inch thickness. Use a cookie cutter to cut into 2-inch rounds. Transfer cookies to baking sheet and sprinkle sesame seeds over half of the cookies. Gently press down sesame seeds. Bake 9-11 minutes. Remove cookies from oven and let cool for 5 minutes before transferring to a cooling rack.
Once cookies are completely cooled, add 2 tsp dulce de leche to the flat side of half of the cookies (without sesame seeds). Top with flat side of remaining sesame seed covered cookies.