Coat an 8- x 8-inch pan with cooking spray.
In a microwave-safe bowl, combine chocolate pieces and condensed milk. Microwave on HIGH until chocolate is melted, stirring every 30 seconds. Be careful not to overcook and scorch chocolate.
Add vanilla and stir until smooth. Spread into pan. Drop peanut butter by tsp. on top of fudge. Swirl with a knife to create marbled design on top. Refrigerate until firm, about 2 hours. Cut into 36 squares and serve.
Nutrition Information per serving:
113 Cal., 5 g. fat, 0 g. fiber
