Mix evaporated milk, sugar, and teaspoon salt in saucepan over medium heat.
Bring to boil; cook for 5 minutes, stirring constantly.
Remove from the heat.
Add marshmallows, butterscotch chips, and vanilla.
Stir vigorously to make sure all the marshmallows melt.
Pour into an 8-inch square buttered pan.
Place into fridge to cool, once cool cut in squares.