Your recipe says:
"Save the empty condensed milk can".
Why? Did I miss something?

Directions
Place a heavy pot on the stove and preheat it over low heat. Add chips
and
milk and stir
until chips are melted and milk combined. Save the empty condensed milk
can.
Stir in vanilla and remove fudge from heat.
Add nuts and currants and stir in immediately. "
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Nancree