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; let 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. Then add the chocolate mixture and beat well. Stir remaining 1 1/2 cups chocolate chips.
Scoop dough onto baking sheets 1 inch apart. Bake at 170 degrees C for 10 minutes. Cool slightly on baking sheets; remove to wire racks to cool completely.