1. Preheat the oven to 350°F and line a baking sheet with parchment paper.

2. Add 1 cup semisweet chocolate chips and the butter to a heatproof bowl, then melt together until smooth.

3. In a mixing bowl, beat the granulated sugar, brown sugar, and eggs until the mixture looks lighter and slightly thickened.

4. Mix in the vanilla extract.

5. Slowly pour the melted chocolate mixture into the egg mixture and stir until smooth.

6. In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt.

7. Fold the dry ingredients into the chocolate mixture just until combined.

8. Stir in the remaining 1/2 cup chocolate chips.

9. Scoop mounds of batter onto the prepared baking sheet, leaving space between each cookie.

10. Sprinkle with flaky sea salt if using.

11. Bake for 9 to 11 minutes, until the tops are crackled and the edges are set.

12. Let the cookies cool on the pan for 5 minutes, then transfer to a wire rack.