Preheat oven to 350 degrees F. In a medium mixing bowl, stir together flour, cocoa, baking powder, and salt. Set aside.

In a heavy medium saucepan, combine the 2 cups chocolate pieces and 2 tablespoons of the butter. Cook and stir over low heat until melted. Set aside to cool slightly.

In a large mixing bowl, beat remaining butter with an electric mixer on medium to high speed for 30 seconds. Add brown sugar; beat until combined, scraping sides of bowl occasionally. Beat in eggs, one at a time, scraping sides of bowl after each addition. Beat in the melted chocolate mixture and vanilla until combined. Add the flour mixture and beat on low speed until well combined. Stir in the 1 cup semisweet chocolate pieces or white baking pieces.

Drop dough by rounded teaspoons 2 inches apart onto ungreased cookie sheets. Bake in preheated oven for 8 to 10 minutes or until edges are firm and surface is slightly cracked. Transfer to a wire rack and cool completely. Dip each cookie one-third to halfway into Chocolate Ganache. Place on wire rack until ganache is set. Makes about 6 dozen.

Combine 1/2 cup whipping cream, 1 tablespoon butter, and 1 tablespoon granulated sugar in a heavy small saucepan. Bring just to boiling, stirring to dissolve sugar. Remove from heat. Place 1 cup semisweet or bittersweet chocolate pieces in a medium mixing bowl. Pour hot cream mixture over chocolate and let stand for 5 minutes. Stir until smooth. Let cool to room temperature before using. Makes about 1-1/4 cups.

Layer between waxed paper in airtight container; cover. Store at room temperature for up to 3 days. Or freeze undipped cookies up to 3 months; thaw and dip in ganache.