Preheat the oven to 375°
Whisk together the flour, baking soda and salt in a bowl.
In a stand mixer, fitted with a paddle attachment, cream the butter on medium speed until light and fluffy, then add the shortening until evenly mixed in. Add sugars and beat for 3 minutes on medium speed. Mix in vanilla. Add eggs one at a time and mix on medium-low speed just until incorporated. Add flour mix until just incorporated. Mix in chocolate. Scoop cookie dough using a portion scoop, I used a 3 ounce scoop. You can make the cookies larger or smaller, but it effect the baking time.
Refrigerate the dough for at least 30 minutes if you are in a hurry, but they improve if you let them sit for 24-36 hours. Resting them will make them taste better, be more uniform in shape and color nicely when they bake.
Bake 6 chilled cookie balls, evenly spaced on a sheet pan in the middle of the oven for about 12- 15 minutes. Sprinkle with flaky sea salt while the cookies are still baking. Do it when they are almost set but not done baking.
Allow the cookies to cool slightly on the pan and then remove to cooling rack.