Combine butter, unsweetened chocolate, and 1 ½ cups of chocolate chips in a large, heavy saucepan. Cook over low heat, constantly stirring, until butter and chocolate melt; let cool.
Combine flour, baking powder, and salt in a small bowl, and set aside.
Beat eggs, sugar, and vanilla at medium speed with an electric mixer. Gradually add dry ingredients to the egg mixture, beating well. Then add the chocolate mixture and beat well. Stir in the remaining 1 ½ cups of chocolate chips.
Scoop dough onto baking sheets 1-inch apart. Bake at 350 degrees for 10 minutes. Cool slightly on baking sheets; remove to wire racks to cool completely.