Prepare a baking sheet by lining it with parchment paper.
In a medium bowl, combine the flour, baking soda and salt. Set it aside.
Add the dark sugar and white sugar to a large mixing bowl and cream together until it’s smooth and well combined.
Add the egg, egg yolk and vanilla extract and mix for one minute
On low speed, add the dry ingredients to the dough 1/3 at a time, mixing well in between.
Use a cookie scoop to drop 2 Tablespoon-size balls into the sugar. Roll around to cover, then place cookie ball on the parchment paper.
Continue with all the dough spacing generously (approximately 3 inches) apart as these cookies spread.
Place the baking sheet in the refrigerator for an hour or up to overnight.
When ready to bake, remove the baking sheet from the refrigerator and preheat the oven to 350 degrees.
Bake the cookies for 14-16 minutes or until the edges are slightly crisp, but the center is still very soft.
Cool on the baking sheet before removing.