1. Place chopped chocolate and butter in a heat proof bowl and melt over a pot with simmering water or in the microwave. Cool to room temperature.
2. In a large bowl, whisk together sugar and eggs. Add the melted chocolate and mix until well combined. Sift flour, cocoa powder and baking powder and mix until combined.
3. Chill in the fridge for 20-30 minutes, until slightly set.
4. Preheat oven to 350°F (175°C). Line 2 cookie sheets or baking trays with parchment paper.
5. Scoop out 1-2 tablespoons of dough, 2-3 inches apart and place onto prepared baking sheets. Lightly spread the dough into a thin layer.
6. Bake in preheated oven for 10 minutes. The edges should be set but the centers should be slightly gooey. The cookies will come out soft from the oven but will harden up as they cool. Cool for 5-10 minutes, then transfer to a wire rack to cool completely.