Preheat the oven to 350°F (175°C). Line baking sheets with parchment paper if desired.

In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.

In a large bowl, combine the browned butter, dark brown sugar, maple syrup, and vanilla extract. Mix until smooth and well combined.

Add the egg and egg yolk, mixing just until incorporated. Do not overmix.

Gradually add the dry ingredients to the wet ingredients, mixing only until no dry flour streaks remain.

Fold in the chopped milk chocolate and dark chocolate until evenly distributed throughout the dough.

*Chill according to your preferred cookie texture.** Cover the dough and refrigerate for up to 30 minutes for thinner, chewier cookies with more spread and crisp, wrinkled edges. For thicker cookies with less spread and a softer, more substantial center, refrigerate for 2 hours or up to overnight. The longer the dough chills, the more the butter re-solidifies, which helps the cookies hold their shape during baking.

Scoop the chilled dough onto the prepared baking sheet, spacing the cookies a few inches apart.

Bake for 12–14 minutes, or until the edges are lightly browned and the centers still appear slightly underbaked.

Immediately after removing the cookies from the oven, sprinkle each cookie with a pinch of flaky sea salt.

Allow the cookies to cool on the baking sheet for 10 minutes before transferring them to a wire rack to cool completely.