In a medium bowl, whisk together the flour, baking soda, and sea salt. This step is crucial as it evenly disperses the leavening agents and salt, ensuring a uniform texture throughout your cookies.
In a large bowl, whisk together the melted butter, brown sugar, and granulated sugar. Make sure to mix until well combined and smooth. This mixture should be glossy and creamy, indicating the sugars are well incorporated.
Add the egg and egg yolk to the butter-sugar mixture. Whisk until the mixture is thick and pale in color, ensuring there are no streaks of egg white left.
Whisk in the vanilla extract, stirring until blended. The warm scent of vanilla will instantly elevate your batter.
Gradually add the dry ingredients to the wet ingredients, using a spatula to mix gently. Be careful not to overmix; you want to combine just until no dry flour remains.
When the dry and wet ingredients are mostly combined, fold in the dark chocolate chips until evenly distributed. This step is where the magic happens; each cookie will be studded with rich chocolate.
Cover the dough with plastic wrap and refrigerate for at least 30 minutes, or up to 2 days. Chilling the dough is essential for texture: shorter chilling yields flatter cookies, while longer chilling results in thicker cookies.
When you’re ready to bake, preheat the oven to 350°F and line two large baking sheets with parchment paper. Make sure your oven is up to temperature for even baking.
Use a 2-tablespoon cookie scoop to drop the dough onto the prepared baking sheets, leaving at least 2 inches between each scoop. This spacing is vital to prevent the cookies from merging as they spread.
Bake one sheet at a time for 9 to 11 minutes, or until the edges are golden brown, but the tops still look pale. They might seem underdone, but they will continue to set as they cool.
Allow the cookies to cool on the baking sheets for 10 minutes before transferring them to a wire rack. This cooling period helps them firm up without falling apart.