- In 4 – 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 – 10 hours, before cutting.