Combine butter, unsweetened chocolate, and 1 1/2 cups chocolate chips in a large heavy saucepan. Cook over low heat, stirring constantly, until butter and chocolate melt; cool.
Combine flour, baking powder, and salt in a small bowl; set aside.
Beat eggs, sugar, and vanilla at medium speed with an electric mixer. Gradually add dry ingredients to egg mixture, beating well. Add chocolate mixture; beat well. Stir in remaining 1 1/2 cups chocolate chips and pecans.
Drop by 2 teaspoonfuls 1 inch apart onto parchment paper-lined baking sheets. (If you don't use parchment paper the cookies WILL stick to the pan.)
Bake at 350° for 10 minutes. Cool slightly and baking sheets; remove to wire racks to cool completely. Yield: about 2 1/2 dozen.