Spray a large cookie sheet with non-stick spray, set aside. In a large pot over medium heat, melt butter or margarine.
Then add mini-marshmallows. Stir them together.
When the marshmallows are mostly melted, add the butterscotch morsels. Stir together quickly but gently.
Lower the heat to low, then quickly stir in the chopped walnuts.
Remove from heat, then dump in the entire 8 cups of cereal.
With a long handled spoon, (I used one of those white plastic spoons) quickly stir in the cereal by going all the way to the bottom of the pot and pulling the lower layers up. Continue to rotate the contents of the pot until the cereal is mixed with the melted goodness.
All at once, dump the hot treats on the prepared cookie sheet. With wet hands, spread out the treats, and pat down to desired thickness or all over the cookie sheet.