Combine chips, condensed milk and marshmallows in the top part of a double boiler over boiling water.
Cover until marshmallows begin to melt.
Stir well until smooth.
Add vanilla and nuts.
Spread in a greased 7x7 pan and let set at room temperature overnight.
Cut into 36 squares.
Separate pieces to let surfaces dry slightly.
Wrap individually in plastic film before packing in refrigerator jars, inexpensive candy dishes or boxes.