Green bean casserole

3 tbsp. evoo divided 6 servings 3/4 c 210 cals
1 med onion half diced half thinly sliced divided
8 oz mushrooms chopped
1 tbsp onion powder
1 1/4 tsp salt divided
1/2 tsp thyme
1/2 tsp pepper
2/3 c flour divided
1 c low fat milk
1 pound frozen French cut green beans about 4 cups
1/3 c sour cream
3 tbsp buttermilk powder
1 tsp paprika
1/2 tsp garlic powder
400 degrees coat a 2 1/2 quart casserole with pam heat 1 tbsp. of oil in large skillet over med heat add diced onions and cook stirring often until tender about 4 mins stir in mushrooms onion powder 1 tsp salt thyme and pepper cook stirring till mushroom juice evaporates 3-5 mins sprinkle 1/3 c flour over the vegetables stir to coat add milk and bring to a simmer stirring often stir in green beans and return to simmer cook till heated 1 min stir in sour cream and buttermilk powder transfer to casserole whisk remaining 1/3c flour paprika garlic powder and remaining 1/4sp salt in a shallow dish add sliced onion to coat heat remaining 2 tbsp. of oil in skillet med heat add onion along with remaining flour mixture and cook turning once until golden and crispy 4-5 mins spread onion topping bake till bubbling about 15 mins let cool