Preheat oven to 350° F. Line two cookie sheets with either parchment paper or silicone baking mats. Set aside.
In a medium bowl, sift together the flour, salt and baking soda. Set aside.
1 1/4 cup all purpose flour, 1/4 teaspoon salt, 1/4 teaspoon baking soda
In a medium sauce pan, over low heat, melt the butter. Remove the pan from the heat and stir in the sugars.
5 Tablespoons butter, 2/3 cup sugar, 1/3 cup brown sugar
Add in the cocoa powder and stir until completely blended.
1/2 cup dark cocoa powder
Add in the vanilla and sour cream. Stir until smooth and almost all lumps are gone.
1 teaspoon vanilla extract, 1/2 cup sour cream
Fold in the flour mixture.
Use a cookie scoop to portion out 1" balls and add 12 per prepared cookie sheet. Gently press down on the dough balls to flatten them. They'll hold their shape.
Sprinkle a bit of sea salt on top of each cookie.
coarsely ground sea salt
Bake for 10 minutes.
Remove them from the oven and let them rest on the cookie sheet for a few minutes before transferring to a wire rack to cool completely.