Preheat the oven to 350°F. Line 2 baking sheets with parchment paper.
Cream butter and sugar. In the bowl of a stand mixer fitted with a paddle attachment, cream together the 1 cup butter, 1 1/2 cups granulated sugar, and 1/2 cup brown sugar on medium speed. Add in 2 eggs and 2 1/2 teaspoons vanilla and mix until smooth.
Make cookie dough. In a separate bowl, whisk together 2 cups flour, 3/4 cup cocoa, 1 1/2 teaspoons baking soda, 1 1/2 teaspoons baking powder and 1 teaspoon salt. Stir in 1 1/2 cups chocolate chips. Gradually add the flour mixture into the wet ingredients and mix on low speed just until combined.
Using a large cookie scoop (or about 2 Tablespoons), spoon dough onto the baking sheet. Press extra chocolate chips on top, if desired. Chill 15 minutes.
Bake 8 to 10 minutes, or until the edges are slightly crisp but still soft in the middle. Let set on the pan 2 minutes before transferring to a wire rack to cool completely. Sprinkle the tops with flaky sea salt, if desired.
Notes
Store: Keep cookies in an airtight container at room temperature for up to 3 days. Let them cool completely before covering.Freeze baked cookies: Store in a freezer-safe bag for up to 3 months.Freeze cookie dough: Scoop dough into balls, flash freeze on a baking sheet until solid, then transfer to a freezer-safe bag. Bake from frozen and add 1 minute to the total baking time.