Start by preheating your oven to 400°F (200°C) and line two baking sheets with parchment paper. This helps the cookies bake evenly and prevents sticking. Preparing the pans in advance also makes the baking process smoother.

In a medium mixing bowl, whisk together the flour, baking powder, and baking soda. This step ensures that the leavening agents are evenly distributed throughout the dough. Proper mixing also prevents clumps in the final cookie batter.

In a large mixing bowl, beat the butter until creamy. Add the dark brown sugar, granulated sugar, and salt, then mix until the texture becomes light and fluffy. This process adds air to the dough and creates a softer cookie texture.

Next, mix in the egg, egg yolk, vanilla extract, and toasted sesame oil. Continue mixing until the ingredients are smooth and fully incorporated. The sesame oil gives the cookies their signature nutty flavor.

Gradually add the flour mixture to the wet ingredients. Mix on low speed until the dough just comes together. Avoid overmixing, as it can make the cookies dense instead of soft.

Scoop about two tablespoons of dough and roll it into balls. Roll each dough ball in sesame seeds so the surface is fully coated. This coating adds texture and enhances the toasted sesame flavor.

Place the cookie dough balls on the prepared baking sheet, leaving space between each one. Bake for 9–11 minutes until the tops are golden and slightly puffed. The cookies will develop a beautiful crinkled texture as they bake.

Once out of the oven, gently press the tops of the cookies with the back of a spatula. Let them rest on the baking sheet for about five minutes before transferring them to a cooling rack.