½ cup butter
4 (1 ounce) squares unsweetened chocolate, chopped
3 cups (18 ounces) semisweet chocolate chips, divided
1 ½ cups all-purpose flour
½ teaspoon baking powder
½ teaspoon salt
4 large eggs
1 ½ cups sugar
2 teaspoons vanilla extract
Combine butter, unsweetened chocolate, and 1 ½ 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 in remaining 1 ½ cups chocolate chips.
Scoop dough onto baking sheets 1 inch appart. Bake at 350 degrees for 10 minutes. Cool slightly on baking sheets; remove to wire racks to cool completely.