Combine butter, unsweetened chocolate, and 1 1/2 cups chocolate morsels in a large heavy saucepan. Cook over low heat, stirring constantly, until butter and chocolate melt; cool.
Combine flour, baking powder, and salt; set aside.
Beat eggs, sugar, and vanilla at medium speed with an electric mixer. Gradually add flour mixture to egg mixture, beating well. Add chocolate mixture; beat well. Stir in remaining 1 1/2 cups chocolate morsels and pecans.
Drop dough by 2 tablespoonfuls 1 inch apart onto parchment paper-lined baking sheets.
Bake at 350° for 10 minutes. Cool slightly on baking sheets; remove to wire racks to cool completely.