chocolate chips (semi-sweet)
or pecans, chopped
In 4 to 6 quart heavy metal pan, cook butter, evaporated milk, and sugar over medium-high heat until sugar is dissolved.
Heat to boiling.
Turn heat to low, cover and continue boiling for 5 minutes without stirring.
Turn heat to warm and stir in marshmallows until dissolved.
Add each kind of chocolate in turn, stirring until melted.
Stir in vanilla and nuts.
Pour into lightly buttered 9x13-inch pan. Let stand until firm, about 8 to 10 hours, before cutting.