Cream the butter, granulated sugar, and brown sugar together until light and fluffy.
1 cup unsalted butter, 1 cup granulated sugar, 3/4 cup light brown sugar
Mix in the eggs and vanilla until fully combined and smooth.
2 large eggs, 2 teaspoons vanilla extract
Whisk together the flour, cocoa powder, baking soda, and salt in a separate bowl.
2 cups all-purpose flour, 3/4 cup unsweetened cocoa powder, 2 tablespoons cornstarch, 1 1/2 teaspoons baking soda, 1 teaspoon salt
Gradually add the dry ingredients to the wet ingredients and mix just until combined.
Fold in the chocolate chunks and chocolate chips evenly throughout the dough.
1 cup chocolate chunks or chopped chocolate, 1 cup chocolate chips
Cover the dough and refrigerate for at least 2 hours or freeze for an hour to prevent spreading.
Preheat the oven to 350 degrees and line baking sheets with parchment paper.
Scoop the chilled dough onto the prepared baking sheets, spacing evenly apart.
Bake until the edges are set and the centers look slightly underbaked.
OPTIONAL: You can add a few chocolate chips to the tops of the cookies as soon as the cookies are removed from the oven.
Cool on the baking sheet briefly, then transfer to a wire rack to cool completely.
OPTIONAL: For perfectly round cookies, swirl a cookie cutter around the warm cookies.