Step 1

Line 8-inch-square baking pan with foil.

Step 2

Combine sugarevaporated milkbutter and salt in mediumheavy-duty saucepan.Bring to a full rolling boil over medium heatstirring constantly.Boilstirring constantlyfor 3 minutes.Remove from heat and stir in vanilla extract and marshmallows.Stir vigorously for 1 minute or until marshmallows are melted.

Step 3

Working fastpour 1/2 cup hot mixture into glass measure.Add white morsels (do not stir); set aside.

Step 4

Working faststir in semi-sweet morsels into saucepan until morsels are just melted.Pour into prepared pan.

Step 5

Stir white morsel mixture until morsels are just melted.

Step 6

Drizzle white morsel mixture over semi-sweet chocolate mixture; swirl with knife for marbled effect.Refrigerate for 2 hours or until firm.Lift from pan; remove foil. Cut into 48 pieces.