Combine first 3 ingredients in large bowl. Mix eggs, sour cream, sugar and vanilla in separate bowl until blended. Add to baking mix mixture; stir just until blended.
Place dough on lightly floured surface. Coarsely chop 2 oz. chocolate; knead into dough just until blended. Shape into ball; flatten slightly. Wrap tightly in plastic wrap. Refrigerate 3 hours.
Roll out dough on lightly floured surface to 1/2-inch thickness. Cut into 16 each doughnuts and holes, using floured 2-1/2-inch round cutter for the donuts and 3/4-inch round cutter for the donut holes.
Heat oil in heavy 3-qt. saucepan or deep fryer on medium heat to 375°F. Carefully add donuts and donut holes, a few at a time, to hot oil; cook 1 to 2 min. or until golden brown. Remove from oil; drain on paper towels. Cool slightly.
Meanwhile, break remaining chocolate into small pieces; place in microwaveable bowl. Add COOL WHIP; stir. Microwave on HIGH 2 min. or until chocolate is almost melted; stir until chocolate is completely melted and mixture is well blended.
Dip tops of warm donuts, 1 at a time, in melted chocolate mixture. Let stand, chocolate-side up, until chocolate is firm.