[header] How to make cheeseburger soup [title] Preheat the oven. [step] To toast the hamburger buns for the crouton topping, the oven must be hot enough. Set the temperature to 400 degrees fahrenheit (200 degrees celsius), and allow it to fully preheat. 
[substeps] If you prefer, you can toast the buns in a toaster oven rather than a standard oven. [title] Spread the bun pieces out on a baking sheet.