In a stand mixer, add the sour cream. Over the stove top, melt the butter in a sauce pan. Remove from heat once completely melted and pour over the sour cream. Using a paddle attachment, mix to combine the butter and the sour cream.
Add the brown sugar and the vanilla to the butter mixture. Mix to combine.
Separate the egg whites and egg yolks, and add the two egg yolks to the stand mixer. Turn the mixer to medium and mix for 1-2 minutes.
In a small bowl, whisk together the flour, baking soda and salt. Slowly add the flour mixture to the wet ingredients, on low speed until just combined.
Add the chocolate chips and on a low speed, mix to combine.
Cover the dough with plastic wrap and let the dough hydrate for 30 minutes in the refrigerator before baking.
With 20 minutes left of rest time for the dough, preheat the oven temperature to 375 degrees.
Line a baking sheet with parchment paper, and using a medium (2 tablespoon) cookie scoop, scoop the cookie dough onto the baking sheet. I typically bake 9 cookies at a time so they don't run into each other during baking. Pop into the oven and bake for 8-10 minutes (watch for golden brown edges), this will yield about 18-20 cookies. You can use a larger ice cream scoop for larger cookies, but only bake about 4 at a time. Using a larger scoop will yield about 12-16 cookies.
Wait a couple of minutes, then use a spatula to move the baked cookies to a cooling rack. ENJOY with cold milk, the best way, of course!