If you haven't browned your butter yet, start with that!  Click Here and follow these instructions and then set it aside to cool.  

You will also need to toast your pecans.  Simply place in a dry skillet on medium heat and stir often until toasted and browned.

Heat oven to 325 degrees. Adjust oven racks to upper- and lower-middle positions. Mix flour, salt, and baking soda together in medium bowl; set aside.

Either by hand or with electric mixer, mix butter and sugars until thoroughly blended. Mix in egg, yolk, milk and vanilla.

*When measuring flour, lightly spoon flour into measuring cups and level with the back of a knife.  If you scoop your flour, it will be too much.  Add dry ingredients to dough. Stir in chips and nuts.

Scoop cookies onto baking sheet.  Bake until cookies are set around outer edges start to firm up yet centers are still soft and puffy, 10-13 minutes (dependent on size).  Sprinkle lightly with flaky sea salt right when they come out of the oven (so it sticks!)  Here is a link to my favorite brand.  Cool cookies on cookie sheets. Serve or store in an airtight container.