In a small bowl, melt the butter, then add the Worcestershire sauce, salt, garlic powder, and onion powder. Whisk to combine well. Pour melted butter over cereal mixture, and stir to evenly coat.
Spread the mix evenly across an un-greased roasting pan or cake pans and bake for about 1 hour. Let cool, then store in an airtight container at room temperature.
Notes
Microwave Option: Combine dry ingredients in a large microwave-safe bowl, pour over the butter mixture, stir well, and cook on full power for 6 minutes, stirring after 2 minutes and again after 4. Do this in a pinch, but be aware that the low and slow heat of the oven yields the richest flavor and crunch.
Baking Sheet: You do not need to use vegetable oil, canola oil, or anything else to coat your pan before cooking the Chex mix. It won't stick.
Storage: Homemade Chex mix keeps well at room temperature for 4-5 days tightly covered. We like to store in my largest tupperware, Stasher bags, or extra-large ziplocks.