Step 1

Line 8-inch-square baking pan with foil.

Step 2

Combine sugar, evaporated milk, butter and salt in medium, heavy-duty saucepan. Bring to a full rolling boil over medium heat, stirring constantly. Boil, stirring constantly, for 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 fast, pour 1/2 cup hot mixture into glass measure. Add white morsels (do not stir); set aside.

Step 4

Working fast, stir 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.