Step 1

To quickly caramelize onions: Heat a skillet over medium heat. Once hot, add the olive oil. Add sliced onions, 1/8 teaspoon salt, and baking soda. Saute for 2 to 3 minutes, until onions start to turn golden. Reduce to medium-low heat. Cook for just 10 to 15 minutes, stirring occasionally, for quick-caramelized onions. The onions are ready when golden and softened. See note #2 for why this method works.

Step 2

Preheat the oven to 400 degrees F.

Step 3

To parboil green beans: Meanwhile, fill a large pot with water. Add 1/2 teaspoon kosher salt. Bring to a boil over high heat. Add trimmed green beans and cook until vivid green but still crisp, about 3 to 5 minutes. Drain and set aside.

Step 4

To make the cream sauce: Heat a large skillet over medium heat. Add two tablespoons of butter. Once melted, add the chopped mushrooms. Cook for 6-8 minutes, until softened. Add the minced garlic and cook until golden and fragrant, about 2 to 3 minutes. Sprinkle in the all-purpose flour. Cook for another 2 minutes, stirring frequently to prevent burning.

Step 5

Using a whisk, slowly stir in the milk. Stir in the vegetable broth. Sprinkle with remaining 1/2 teaspoon salt and pepper. Once the mixture starts bubbling over medium heat, reduce to medium-low. Simmer until thickened, stirring occasionally, about 6 to 8 minutes. It should be thick enough to coat the back of a spoon without sliding off.

Step 6

Assembly: Lightly coat an 7x11 inch or 2-quart casserole dish with non-stick spray or oil. Evenly layer the cooked green beans across the bottom. Cover with the caramelized onions. Pour the sauce over the green beans and onions, spreading to fully cover the green beans. Sprinkle the top with the fried onions.

Step 7

Cover with foil. Bake at 400 degrees for 25 minutes total. Take the foil off for the last 10 minutes. The casserole is ready when it is bubbling and the fried onions are golden brown. Enjoy!