Prepare all of the ingredients. Preheat oven to 400deg.
In a sauce pan over medium heat, add butter, thyme, tarragon and rosemary. Once melted, whisk in flour and cook for 3 minutes. Then whisk in chicken broth and cook for 3 minutes. Last whisk in heavy cream and cook for 3 minutes.
In a 13x9 baking dish, add bratwurst, potatoes and green beans. Pour cream sauce over top and toss to combine. Sprinkle wiht parmesan cheese and french fried onions. Then put in oven to bake for 30 minutes. Let rest for 5 minutes before serving.