melt chocolate and butter
On a stove or in a microwave, melt the chocolate and butter together. Stir, then set aside to cool to room temperature. Line two cookie sheets or baking sheets with parchment paper.
Combine everything together
In a small bowl, combine all-purpose flour, baking powder, and a pinch of salt. In a large bowl (or in a bowl of a stand mixer), beat the eggs, white and brown sugar using an electric mixer until you get a nice, pale mixture, for about 3 minutes. Add the melted (cooled) chocolate and butter mixture and continue to mix until combined. While continually mixing with an electric mixer (or using a stand mixer) gradually add in the dry ingredients and mix until the mixture is thick and combined.
cookie dough rest
Leave the cookie dough in a bowl. Cover with a plastic wrap or cling film and place in the fridge for 1 - 2 hours (or overnight) or place in a freezer for 30 minutes to chill. It’s easier to work with chilled cookie dough.
shape into cookies
Preheat your oven to 180 °C / 350 °F. Using a small ice cream scoop, scoop some dough and roll in into a walnut-sized ball between the palms of your hands. (approx. 1-inch or 2.5 cm in diameter or 20g). Working in batches of two, place each cookie on a large baking sheet, lined with parchment paper. Make sure to leave enough space between the cookies because they will spread. Gently press the cookie down to prevent them from rolling.
Place the baking sheet with cookies into the preheated oven on the middle rack and bake for about 8 - 10 minutes at 180 °C / 350 °F or for 8 - 10 minutes at 165 °C / 330 °F, if you are using a fan, assisted oven. The cookies should be soft when you take them out of the oven because they will harden as they cool. Make sure not to overbake them. Transfer baked chocolate brownie cookies to a wire rack to cool. Serve or store in a cookie box for up to 14 days.