Step 1

Whisk flour, baking soda, cornstarch, and salt in a medium bowl.

Step 2

Using an electric mixer, beat eggs, oil, tahini, and vanilla in a large bowl on medium speed until creamy and emulsified, about 2 minutes. Beat in granulated sugar and brown sugar until combined, about 45 seconds. Reduce speed to low and beat in dry ingredients, chopped dates, and three quarters of chocolate, scraping down sides of bowl as needed, just until combined, about 30 seconds. Cover dough and chill at least 3 hours and up to 12 hours.

Step 3

Place a rack in middle of oven; preheat to 375°. Using a #10 cookie scoop (about 6 Tbsp.), portion out dough onto 2 parchment-lined baking sheets, spacing 3" apart. Top with remaining chocolate and press gently to adhere. Gently press 1 date quarter into top of each cookie. Sprinkle with sea salt.

Step 4

Working with one baking sheet at a time, bake cookies until golden brown around the edges, 13–15 minutes. Let cookies cool 5 minutes on baking sheets, then transfer to wire racks and let cool completely.