Healthy Green Bean Casserole

Preheat the oven to 400°F. Thinly slice the onion, toss with 1 tablespoon oil and the panko, and bake on a sheet pan for 15 minutes, stirring once, until crisp. 2. Trim the green beans and blanch in boiling salted water for 4 minutes. Drain and rinse with cold water. 3. Heat the remaining oil in a skillet. Cook the sliced mushrooms for 6 to 7 minutes, then add the garlic. 4. Sprinkle in the flour and stir for 1 minute. Slowly whisk in the broth and milk and simmer until thickened, about 4 minutes. Season with salt and pepper. 5. Stir in the green beans and pour into a baking dish. Top with the crispy onions and parmesan. 6. Bake at 375°F for 15 minutes until bubbling.