Chef John’s Classic Green Beans Au Gratin

The best green bean casserole! Welcome back to my Thanksgiving series! Recipe from @Destiny Dezaray Ingredients: 2 tbsp butter 1 diced yellow onion 1 cup diced mushrooms 2 tbsp minced garlic 7 crumbled bacons Sprinkle of salt Sprinkle of pepper 1 tsp paprika 1 tsp dried parsley 1/2 tsp dried rosemary 3 more tbsp butter 3 tbsp all purpose flour 2 cups heavy cream 1/2 cup chicken broth 1/2 cup shredded Mozerella 3 cans green beans Topping: 1/2 cup Mozerella cheese 1 bag kinders crispy onions 4 cru