PREHEAT oven to 350�F. Grease 9-inch-round cake pan. Line bottom of pan with parchment paper; grease.
COMBINE eggs and sugar in large bowl. Stir in flour, melted butter, unsweetened chocolate, vanilla extract and salt until smooth. Pour into prepared pan.
BAKE for 25 minutes or until a wooden pick inserted in the middle comes out clean. Cool on wire rack for 5 minutes. Run knife around edge of cake; cool for an additional 10 minutes. Invert cake onto serving platter. Remove pan and parchment; cool completely.
FOR PEANUT BUTTER LAYER:
BEAT peanut butter, butter and vanilla extract in medium mixer bowl until combined. Gradually beat in powdered sugar. Spread mixture on cake. Refrigerate for 30 minutes.
HEAT cream in small saucepan to boiling; remove from heat. Add semi-sweet morsels; let stand 5 minutes. Stir; refrigerate for 30 minutes or until mixture is spreadable. Spread chocolate on top and sides of cake.
MELT peanut butter & milk chocolate morsels in resealable plastic bag on 70% power for 30 seconds. Knead bag to mix. If necessary, microwave at additional 10- to 15-second intervals until melted. Cut a small hole from corner of bag; squeeze to drizzle over cake. Store in refrigerator. Let stand for 30 minutes before serving.