Step 1: Preheat your oven to 250°F (120°C). In a small microwave-safe bowl or saucepan, melt the butter. Stir in the Worcestershire sauce, seasoned salt, garlic powder, and onion powder until well combined.
Step 2: In a very large roasting pan (or two large baking sheets with high sides), combine the Rice Chex, Corn Chex, Wheat Chex, mixed nuts, pretzels, and broken bagel chips. Gently toss to mix.
Step 3: Slowly pour the melted seasoning butter mixture over the cereal and nut mixture. Using a large spoon or spatula, gently fold and stir until all ingredients are thoroughly and evenly coated.
Step 4: Spread the coated mixture in a single, even layer in the roasting pan. If using baking sheets, divide the mixture evenly between the two sheets.
Step 5: Bake for 1 hour, stirring gently every 15 minutes to ensure even toasting and to prevent burning. The low temperature allows the flavors to meld and the mix to crisp up.
Step 6: Remove the Original Homemade Chex Party Mix from the oven. Immediately spread it out on paper towels or a large sheet of parchment paper to cool completely. This helps drain any excess butter and ensures maximum crispness.
Step 7: Once completely cooled to room temperature, store the party mix in an airtight container. It will remain fresh and crunchy for up to 2 weeks.