- Preheat the oven to 180 °C (350 °F).
- On a baking sheet, toast the pecans in the middle of the oven, taking care to stir them from time to time. Set aside.
- In a saucepan, over low heat, melt the chocolate and butter. Remove from the heat.
- In a bowl, sift together the flour and baking powder. Set aside.
- In another bowl, beat the eggs, sugar and vanilla with an electric mixer on high speed, until the mixture is light and fluffy, about 5 minutes. Stir the melted chocolate into the egg mixture while mixing on medium speed until the mixture is smooth. Stir in the dry ingredients on low speed.
- With a wooden spoon, fold in the semisweet and white chocolate and pecans. For each cookie, place a generous 30 ml (2 tablespoons) of dough on a buttered baking sheet. Refrigerate the remaining dough for another batch. Bake in the middle of the oven for 12 to 14 minutes. Cool for 2 minutes before removing from the baking sheet. Cool completely on a rack.