1. Preheat your oven to 350°F (175°C) while you prepare your cookie dough.
2. In a mixing bowl, combine the softened unsalted butter, dark brown sugar, and granulated sugar. Use a whisk or spatula to cream them together until the mixture is light and fluffy.
3. Mix in the egg yolk and vanilla extract until fully incorporated, ensuring a smooth texture.
4. In a separate bowl, whisk together the all-purpose flour, fine grain sea salt, and baking soda. Gradually add this dry mixture to the wet ingredients, stirring until just combined.
5. Gently fold in the dark or semisweet chocolate chips, being careful not to overmix.
6. Using a cookie scoop or tablespoon, drop rounded portions of dough onto your prepared baking sheet. Leave enough space between each cookie as they will spread slightly while baking.
7. Place the baking sheet in the preheated oven and bake for about 8-10 minutes, or until the edges are golden but the centers are still soft.
8. Remove the cookies from the oven and let them cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.