Place butter in a medium saucepan (I think a light colored pan like All-Clad works best so you can see the color of the butter changing) over medium-low heat.
Melt the butter and cook, swirling occasionally, as it progresses from lemony-yellow color to golden, then to amber. Once it is amber and you see little flecks of brown on the bottom of the pan, immediately remove it from the heat. Let it cool for 30 minutes.
Once cooled:
In large bowl with electric mixer, combine butter with brown sugar and granulated sugar, and beat until well combined, about 3 minutes.
Add vanilla, egg, and egg yolk, and beat until combined, about 1 minute.
Add flour, salt, and baking soda, beating until incorporated.
Fold in the chocolate chunks.
Chill dough in the refrigerator for at least 30 minutes.
Once dough has chilled, preheat oven to 350 degrees F.
Line baking sheet with parchment paper.
Scoop dough into 1" balls (approximately 1.5-2 tablespoons) and place 2" apart. The dough will spread.
Sprinkle with sea salt.
Bake in preheated oven for 11-13 minutes, until golden brown around the edges. Let cool on cookie sheet for 5 minutes then transfer to cooling rack.
Very important: eat at least two immediately with a glass of cold milk.
Hide the rest from everyone else in your household in an airtight container. Okay, maybe share a couple.
Enjoy!