In a microwave-safe bowl combine butter (1/2 cup) and both chocolates (4 ounces unsweetened chocolate + 1 1/2 cups semisweet chocolate chips). Microwave for 1 1/2 minutes at 50% power. Remove and stir ingredients to combine. If ingredients aren't melted after being well stirred, microwave for 30 seconds and remove then stir again. Set aside.
In a small bowl combine flour (1 1/2 cups), baking powder (1/2 teaspoon), and salt (1/2 teaspoon). Set aside.
In a large bowl beat eggs (4), sugar (1 1/2 cups), and vanilla (2 teaspoons) with an electric mixer at medium speed. Gradually add flour mixture, beating until well combined. Add chocolate mixture and beat until well combined. Stir in pecans (2 cups).
Spoon dough by 2 tablespoonfuls onto Silpat or parchment-lined baking sheets allowing 1-inch spacing between cookies.