In top of a double boiler: 
12 oz pckg semi sweet chocolate
 14 oz can condensed milk
 2 Tbsp butter or margarine 
When melted, remove from heat. 
In a large bowl combine: 
2 c dry roasted peanuts 
10 1/2 oz pckg mini marshmallows 
Fold in melted chocolate. 
Spread in a wax paper lined 13x9 pan. 
Chill 2 hours. 
Remove from pan, peel off wax paper. 
Cut into squares. 
Cover & store at room temp.