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.
Cover empty condensed milk can with plastic food wrap and center it in the greased cake pan. Spoon fudge into pan around can, making sure to recenter can if it drifts.