1. Heat oven to 350 degrees F. Grease a 9-inch square pan; set aside.
2. Combine 1 cup of the chocolate chips, the unsweetened chocolate and butter in microwave proof bowl. Microwave on 100 percent power (High) 1 to 1-1/2 minutes; stir until smooth. Whisk in the 3/4 cup sugar, 2 eggs and the 1/8 teaspoon vanilla. Stir in the 1/2 cup flour and the salt until well combined.Make Peanut-Butter Filling::
3. Beat all filling ingredients together in large bowl on medium speed of electric mixer until smooth.
4. Spread half of the chocolate batter in prepared pan. Drop Peanut Butter Filling over batter; spread evenly. Spread on remaining chocolate batter. Bake 30 minutes until toothpick inserted in center comes out barely clean. Sprinkle top with remaining 1/3 cup chocolate chips. Let stand 3 minutes to soften chips; spread over top. Cool completely and refrigerate until firm. Cut into 2-1/2x2-inch squares. Makes 12 brownies.