In a VERY large bowl (or two smaller ones), combine pretzels, cereal and peanuts.
In a small saucepan, bring brown sugar, butter and corn syrup to a boil at a low temperature. Boil 2-3 minutes, stirring constantly. Be careful not to burn.
Add vanilla, baking soda and cream of tartar. Bring back to a boil. Your mixture will almost look light and fluffy. Remove from heat and pour over your pretzels, cereal and peanuts.....coating as evenly as possible. It may be necessary to do this in smaller batches.
Bake on 2 jelly roll pans for 5 minutes. Stir and bake another 5 minutes. Cool. Break apart and mix in M&M's. This is SOOOOO good!