First made for the Hughson High School Husky Soccer Team, 1995 - 1996.
SKOR Toffee Bits can be bought on Amazon in 3lb. bags, good for about 9 recipes. About $28 as of 2021. I haven't seen them in stores in years. You can use other toffee bits instead of the SKOR, but they are not nearly as good.
In order to maintain consistency, I use a food scale to weigh the ingredients, except for the butter where I go by the markings on the paper.
How large a microwave dish? The one I use is an old 4-qt Anchor-Hocking pot made for microwaves, and it's almost too small! 
Store toffee bits at 65°F or below (but not frozen) in an airtight container.

In a bag or other container, mix together everything but the marshmallows and the butter.
Set aside.
In a large, microwave dish (see comments), melt the butter, about 1 minute. 
Add marshmallows, tossing generously so that they are well coated with the melted butter.
Microwave for about 3 minutes or until marshmallows have doubled in volume.
Don't overdo it or your treats will be in the break-your-teeth stage!
Stir dry ingredients into marshmallows, mixing thoroughly.
Spread evenly into a baking dish or onto a cookie sheet, which should be well coated with butter.
Coat your hands with butter and smooth out the top of the Husky Treats.
I also use a buttered rolling pin.
Allow to cool and then cut them up and serve.
Serving size says 16 2" squares, but I usually cut them in 1" squares.