Sift together flour, cocoa powder, baking powder and salt in a medium bowl. Set aside.

Melt the chocolate in the microwave for about 1 minute. Stir. Continue to melt in 30 second increments until fully melted and smooth. Set aside.

In a small bowl, whisk the eggs and vanilla. Set aside. With an electric or stand mixer with paddle attachment, beat the butter until smooth and creamy—about 1 minute. Beat in the sugars, scraping down the sides every 10 seconds or so. The mixture will be granular.

Mix in the beaten egg/vanilla until incorporated. Add the chocolate in a steady stream and beat until combined. Add the dry ingredients on slow speed. Fold in the chocolate chips and peanut butter chips. Do not overmix at any point in this process.

Chill dough for at least 30 minutes. Preheat oven to 350°F (177°C). Line two large baking sheets with parchment paper or silicone baking mats.

Scoop about 2 Tablespoons of dough and roll into a ball. Bake for about 10 minutes, or until the cookies have just begun to set with the centers still appearing very soft. They will firm up as they cool.

Allow cookies to cool on baking sheet for at least 5 minutes before transferring to a wire rack to cool completely. Cookies stay fresh and soft at room temperature in an airtight container for up to 7 days. Cookies freeze well, up to 3 months.