Step 1

Heat the oven to 350°F with racks in the upper- and lower-middle positions. Line 2 baking sheets with kitchen parchment. In a 12-inch skillet over medium, combine both sesame seeds and toast, stirring frequently, until the white seeds are golden brown, 8 to 10 minutes. Transfer to a small bowl and let cool completely; wipe out but do not wash the skillet.

Step 2

Set the empty skillet over medium and melt the butter. Cook, swirling the pan frequently, until the milk solids at the bottom are browned and the butter has a nutty aroma, 1 to 3 minutes. Immediately pour into a medium heatproof bowl and let cool for 10 to 15 minutes. Meanwhile, in a small bowl, whisk together the flour and baking soda; set aside.

Step 3

To the butter, whisk in the tahini, sugar and salt; the sugar will not fully dissolve. Whisk in the egg. Using a rubber spatula, stir in the sesame seeds. Add the flour mixture and stir until combined.

Step 4

Form the dough into thirty 1-inch balls (1 rounded tablespoon each), rolling the dough between the palms of your hands. Arrange 15 balls on each prepared baking sheet, evenly spacing them. Using the palm of your hand, flatten each into a disc about ¼ inch thick.

Step 5

Bake until light golden brown at the edges, 12 to 14 minutes, switching and rotating the baking sheets halfway through. Let cool on the sheets for 5 minutes, then transfer to wire racks and cool completely.