Preheat oven to 325 degrees F. Grease two large cookie sheets. In a small bowl, combine flour, cocoa, baking powder and salt.
In heavy 2-quart saucepan, melt chocolate and butter over low heat, stirring frequently, until smooth. Remove from heat and cool.
In large bowl, with mixer at medium speed, beat eggs and sugar until light and lemon colored, about 2 minutes, frequently scraping bowl with rubber spatula. Reduce speed to low. Add cooled chocolate mixture, flour mixture, and vanilla; beat until just blended. Increase speed to medium; beat two minutes. With wooden spoon, stir in pecans and chocolate chips.
Drop batter by rounded teaspoons, 2 inches apart, on prepared cookie sheets. With small metal spatula or back of spoon, spread batter into 2inch rounds. Bake until tops are shiny and cracked, about 13 minutes; rotating cookie sheets between upper and lower oven racks halfway through baking. Cool 10 minutes on cookie sheet. With wide metal spatula, transfer cookies to wire racks to cool completely.
Repeat with remaining batter.