MELT 1/4 cup (4 Tbsp.) butter; mix with wafer crumbs until blended. Press onto bottom and up side of 9-inch tart pan with removable bottom. Bake 10 min.; cool.
MEANWHILE, mix sugar and cornstarch in medium saucepan. Gradually whisk in water until blended. Bring to boil on medium heat. Cook 5 min., stirring constantly. Remove from heat. Add dry gelatin mixes; stir 2 min. until gelatin is completely dissolved. Add remaining butter; stir until melted. Refrigerate 30 min. or until slightly thickened, stirring occasionally. Pour into crust. Refrigerate 3 hours or until firm.
RUN knife around tart to loosen from rim of pan; remove rim. Microwave jam in microwaveable bowl on HIGH 15 sec. Arrange mango slices on tart; brush with jam.