1. Line a 9x13 baking dish with parchment paper.
2. Put chips, butter, and sweetened condensed milk in a large heavy saucepan over low heat, and stir together constantly until chocolate and butter is melted and mixture is smooth. Take off heat immediately.
3. Toss together the peanuts and marshmallows in a separate bowl, then add the chocolate mixture and stir together well.
4. Turn mixture into parchment lined baking dish and spread evenly.
5. Place pan in cool area (not refrigerator) until mixture becomes firm.
6. Lift mixture out of pan by edges of paper onto a cutting board. Peel paper from candy and cut candy into little squares for serving. Arrange on a plate or platter, cover lightly, and keep in a cool dry environment, not a refrigerator.
If you thought you could never make candy, think again. This is the simplest method to make this classic candy I've ever seen.
I mention twice not refrigerating the candy. The reason is because refrigerators harbor moisture, as they should for most things, but not for chocolate. Chocolate that's exposed to moisture will get funny looking. All chocolate needs to set up is a cool area. A back hall closet that isn't heated may be just right.