Best Fudge Ever!

This is my grandma's recipe and it is SO good! It's really easy to make. The trick is to continually stir while boiling.

3 cups white sugar
2/3 cup evaporated milk
3/4 cup margarine
1 pkg marshmallows (11oz) or 6 cups mini marshmallows
2 cups chocolate chips
1 cup chopped nuts (optional)
1 tsp vanilla

Combine sugar, margarine and milk in saucepan. Bring to full or rolling boil. Stir constantly.
Continue boiling for 5 mins over medium heat- stir, stir, stir!
Remove from heat, stir in chocolate chips until melted. Add marshmallows and mix. Add vanilla and nuts.
Beat until well blended.
Pour into greased 9x13 pan.
Leave on counter at room temperature to cool.
Cut into squares.
Enjoy!