The Best Fudge Ever

1/4 cup butter
7 oz marshmallow cream
1 1/2 cups sugar
2/3 cup evaporated milk
1/4 teaspoon salt
12 oz semi-sweet chips
1 teaspoon vanilla

Melt butter over medium heat in a heavy saucepan. Add marshmallow cream, sugar, evaporated milk and salt. Stir constantly and allow to boil for 5 full minutes (watch your hand, it may get burned if the boiling mixture pops). After boiling for 5 minutes, remove from heat and stir in semi-sweet chips until completely melted (this may take another 5 minutes until they melt completely). Add vanilla, stir. Pour into an 8x8 inch pan that has been lined with a double layer of plastic wrap. Chill until firm. Cut into pieces. Keep refrigerated until ready to eat.