In a microwave-safe bowl, combine 1/2 cup of chocolate chips and butter. Heat for 1 minute at full power, stir and then continue to heat at 20 second intervals, stirring between each until chocolate has melted. Set aside to cool slightly.
In a separate bowl, whisk together the egg, vanilla and sugar briskly until thick and pale, this may take a few minutes. Stir in the chocolate mixture. Combine the flour, baking powder, cocoa powder and salt; whisk into the batter just until blended. Fold in the nuts, remaining chocolate chips and raisins. Cover and chill dough for 1 hour.
Preheat the oven to 325 degrees F (175 degrees C). Line baking sheets with parchment paper or grease lightly. Scoop out heaping tablespoonfuls of dough and roll them into balls. Place them 2 inches apart on the baking sheets and flatten slightly.
Bake in the preheated oven until slightly puffed and just set, 13 to 15 minutes. Set the baking sheet on a cooling rack to cool. Cookies will firm up as they cool.