Add the chopped bittersweet chocolate and unsalted butter to a microwave-safe bowl. Microwave in 20-second intervals, stirring thoroughly after each one, until the mixture is smooth and glossy. Set it aside for about 5 minutes to cool slightly.

Place the granulated sugar, brown sugar and room-temperature eggs in a large mixing bowl. Beat with a hand mixer or stand mixer for about 4 minutes. The mixture should become lighter in colour, thick and noticeably frothy. This step helps create those shiny, crackled brownie-cookie tops.

Pour the slightly cooled chocolate mixture and vanilla extract into the whipped eggs and sugar. Mix on low speed just until the batter looks smooth and evenly combined.

In a separate medium bowl, whisk together the all-purpose flour, cocoa powder, baking powder, salt and instant espresso powder.

Add the dry ingredients to the chocolate mixture. Fold gently with a spatula until only a few small streaks of flour remain. Add the semisweet chocolate chips and continue folding just until everything is combined. Do not overmix.

Cover the bowl and refrigerate the chocolate brownie cookie dough for 35 to 45 minutes. It should feel thicker and be firm enough to scoop, but it should not become hard.

Preheat the oven to 350°F (180°C). Line two large baking sheets with parchment paper.

Scoop approximately 2 tablespoons of dough for each cookie. Place the dough portions on the prepared baking sheets, leaving about 3 inches of space between them because they will spread.

Bake for 9 to 11 minutes, or until the cookies have spread and the tops look shiny and cracked. The edges should appear set, but the centres will still look slightly soft. That is what gives these cookies their fudgy brownie texture.

Leave the cookies on the pans for at least 15 minutes before moving them. They are quite delicate when warm but will firm up as they cool while staying soft and chewy in the centre.