Super Chunky Chocolate Cookie Recipe

1 cup all-purpose flour

2/3 cup natural cocoa powder

1/2 teaspoon baking soda

1/4 teaspoon salt

1/2 cup unsalted butter, plus 2 tablespoons

3/4 cup muscovado sugar

1/4 cup sugar

2 teaspoons vanilla extract

2 large eggs

1 cup semisweet or bittersweet chocolate, roughly chopped

rock salt, for topping