Position 1 rack in the top 1/3 and another in the bottom 1/3 of the oven and preheat to 350 degrees F. Line 2 baking sheets with parchment paper.
Sift together the flour, baking soda and salt into a medium bowl and set aside. Melt the chocolate and butter in the top of a double boiler over hot, simmering water. Remove from the heat but keep the chocolate mixture over a bowl of hot water to ensure that the mixture does not set.
In a small bowl, combine the vanilla extract and the espresso powder and whisk until the espresso powder is dissolved. Stir the espresso mixture into the chocolate mixture.
Combine the eggs and both sugars in the 4 1/2 quart bowl of a heavy-duty electric mixer. Set the bowl over a pan of hot, hot simmering water. Stir with a hand-held wire whisk until warm to the touch. Attach the bowl to the mixer stand. Using the wire whip attachment, whip the mixture on high speed until pale, thickened and cool, about 5 minutes. Fold into the warm chocolate mixture. Fold in the flour. Stir in the chocolate chips and pecans.
Drop the dough by rounded tablespoons onto the 2 prepared pans leaving about 1 to1/2 inches between the cookies. Bake for 12 to14 minutes or until the cookies are set: switch the positions of the baking sheets halfway through the baking time for even baking.
Cool the cookies on the baking sheets on wire racks for about 3 minutes, then transfer the cookies to wire racks to cool completely. Repeat with the remaining dough.