Preheat oven to 360 F. Line a quarter sheet pan (or a half) with parchment paper.
In a bowl, use a hand mixer to beat together the butter and brown sugar on medium until light and fluffy, at least 3 minutes.
Add the soda and vanilla and beat for another two minutes.
Add the egg yolk, beat for one minute.
Add the flour and beat to just combine. Fold in the chocolate.
Divide dough into six equal balls. If you use a cookie scoop you’ll get the pretty ridges, use a 1 1/2 tablespoon size, slightly heaped. Place on cookie sheet. Sprinkle with sea salt if desired.
Bake for 10 minutes, don’t wait for them to get color on top or they will be overdone. Allow to cool on the pan before moving. Store in an airtight container.