Brown Butter: Place 1/2 cup (1 stick) of butter in a medium skillet. Melt over medium heat, swirling the pan frequently, as it begins to foam and froth and develop a nutty smell. Once it turns light golden/amber colored, remove from heat and pour into a small bowl. Allow it to cool to room temperature before making the cookie dough.

Cookie Dough: Add remaining stick of butter to a mixing bowl with brown sugar and mix for 3 minutes, until fluffy and smooth. Add granulated sugar, cooled browned butter and vanilla extract and mix well. Add egg and egg yolk and mix. Add the flour, salt, baking powder, and baking soda, mixing on low speed just until incorporated. Stir in chocolate chunks.

Chill dough: Cover the dough with plastic wrap and refrigerate for at least 20 minutes. Preheat oven to 350°F and line two baking sheets with parchment paper.

Scoop 2 tablespoon-size portions of dough and roll into balls. Place on prepared baking sheets, 2 inches apart.

Bake for 11 to 14 minutes, or until just barely golden on the edges.

Remove from oven and cool on the baking sheet for 5 minutes before transferring to a wire cooling wrack to cool completely. Sprinkle the tops with a sea salt or flake salt, if desired.