In a bowl, whisk together the baking soda, salt and flour. Set aside.
Place the butter and brown sugar in a stand mixer fitted with a paddle attachment. Beat on medium-high speed until light and fluffy, 3 to 4 minutes.
Add egg and yolk one at a time, mix until smooth on low speed. Beat in vanilla.
Slowly mix in dry ingredients, being careful not to over mix. I usually stop when I still have some flour remnants around the bowl.
Chop up the chocolate bars into chunks, trying to keep some large and some small for different variants of size. Stir the chocolate into the dough until combined.
Scoop the dough into large balls, I like to use the ¼ cup cookie or ice cream scoop. At this point you can either have the patience to chill the dough knowing the results which be better, or bake your cookies because you just can't seem to resist. I like to scoop out all the balls and lay them out on a parchment lined cookie sheet, and then refrigerate for at least 2 hours.
When ready to bake, turn the oven on to 350 F, and line 2 cookie sheets with parchment paper. Place 8 chilled cookie dough balls on the cookie sheet, sprinkling with the flaked sea salt. Some people salt their cookies after they bake them, but I like to do both. This gives the salt that falls off the tops an opportunity to bake underneath the cookie and give even that much more flavor.
Bake the cookies for 11-13 minutes. You're looking for a nice golden brown outside, with a slightly glossy texture to the inside. If your cookies don't come out in a perfect circle, I like to take a spatula and circle the rim of the cookie to bring in any spots that have spread a little too far.
I prefer to only bake the amount of cookies we are going to eat at the time, which is usually one pans worth. Freeze the rest of the dough balls in a ziplock, and pull out whenever you're craving a warm cookie or two.