In 1-quart heavy saucepan, mix Fudge Layer and Sauce ingredients. Cook over medium-low heat, stirring constantly, until chips are melted. Remove from heat; stir until smooth. Reserve 2 tablespoons fudge mixture in small microwavable bowl for drizzle; cover and refrigerate until needed. Spread remaining mixture in bottom of cooled baked pie shell. Refrigerate 10 minutes.