Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large bowl, cream together 1 cup softened butter, 1 cup granulated sugar, and 1 cup brown sugar until light and fluffy, about 3-4 minutes.
Add 2 eggs one at a time, beating well after each addition. Mix in 2 teaspoons vanilla extract.
In a separate bowl, whisk together 2 cups flour, 3/4 cup sifted cocoa powder, 1 teaspoon baking soda, 1/2 teaspoon baking powder, and 1/2 teaspoon salt.
Gradually add dry ingredients to butter mixture, mixing on low until just combined. Don't overmix.
Fold in 2 cups chocolate chips and 1 cup chopped chocolate by hand using a spatula.
Scoop rounded tablespoons of dough onto prepared sheets, spacing 2 inches apart.
Bake for 10-12 minutes until edges are set but centers look slightly soft.
Cool on baking sheet for 5 minutes, then transfer to wire rack. Sprinkle with flaky sea salt if desired while still warm.