Step 1: Preheat your oven to 350°F (177°C). Line a baking sheet with parchment paper.
Step 2: In a microwave-safe bowl, melt the unsalted butter and 12 oz semi-sweet chocolate chips together. Heat in 30-second intervals, stirring until smooth. Let the mixture cool slightly.
Step 3: In a separate bowl, whisk together the granulated sugar, brown sugar, eggs, and vanilla extract until well combined.
Step 4: Stir the sugar-egg mixture into the cooled chocolate mixture until fully incorporated.
Step 5: Sift the all-purpose flour, cocoa powder, baking powder, and salt into the wet ingredients. Fold gently until just combined, being careful not to overmix.
Step 6: Chill the cookie dough in the refrigerator for 15 minutes. This helps the cookies maintain their shape.
Step 7: Scoop about 2 tablespoons of dough for each cookie. Flatten slightly in your palm, place a few additional chocolate chips in the center, and then form the dough around the chips into a ball. Place on the prepared baking sheet, leaving some space between each cookie.
Step 8: Bake for 10-12 minutes, or until the tops are glossy and cracked and the edges are set but the centers still look soft and slightly gooey.
Step 9: Cool on the baking sheet for 5 minutes before carefully transferring to a wire rack to cool completely. The centers will firm up slightly as they cool, but remain wonderfully gooey when warm.