PREHEAT oven to 325°F. Lightly grease and flour large baking sheet. Reserve 1/2 cup of the chocolate. Microwave remaining chocolate in small microwavable bowl on HIGH 2 minutes. Stir until chocolate is completely melted; cool slightly. Mix flour, baking powder and salt in medium bowl; set aside.
BEAT butter and sugars in large bowl with electric mixer on medium speed until well blended. Add eggs, 1 at a time, beating well after each addition. Blend in melted chocolate and vanilla. Gradually add flour mixture, beating well after each addition. Stir in almonds. Divide dough in half. On floured board, shape each half into 10x2-inch log. Place, 2 inches apart, on prepared baking sheet.
BAKE 40 to 50 minutes or until toothpick inserted in center comes out clean. Cool on baking sheet 15 minutes. Place logs on cutting board; diagonally cut each log into 18 slices using serrated knife. Place slices, cut sides down, on baking sheet. Bake an additional 20 minutes, turning biscotti over after 10 minutes. Remove to wire racks; cool completely.
MELT reserved chocolate as directed on package. Drizzle over biscotti. Let stand until chocolate is firm.