1.If you plan on frying your own onions, begin heating a saucepan of canola oil over medium-high heat. The oil should be about 1 to 2 inches deep and slightly smoking when it is ready to fry.

Preheat the oven to 350°.

2. Melt the butter in a large skillet over medium heat. Add the mushrooms, stir to coat with the butter, and sprinkle with 1/4 tsp kosher salt.  Cook over medium-low heat for about 10 minutes, until the mushrooms are soft and dark.

3. Make the batter for the fried onions: In a small bowl, mix together the flour, salt, and spices with a fork. Add a cup of flour and mix. Add additional water, a tablespoon at a time, until the mixture is the consistency of a creamy soup. Stir in the onions, tossing to evenly coat the onions with the batter. Set aside until the oil is hot and slightly smoking.

2. Sprinkle flour evenly on the darkened mushrooms and stir. Slowly pour in the milk and cream, whisking the liquids into the mushroom roux as you pour. Heat over medium-low heat for 5 to 10 minutes, or until the sauce has thickened. Taste and add salt as needed. Add green beans and stir to coat the beans with the mushroom sauce. Transfer the bean mixture into a long baking dish. Bake for 25 minutes in preheated oven.

5. Fry the onions: Test the oil to see if it is the right temperature by dropping one battered onion in the oil. The onion should immediately sizzle and should be brown and crisp in 5 to 10 seconds. If it immediately darkens, the oil is too hot. If the onion takes longer than about 10 seconds to fry, the oil needs to be hotter. If the oil is not hot enough, the onions will take too long to cook and soak up oil making them soggy. Once the oil is the correct temperature, use a fork to transfer the battered onion slices into the hot oil in two batches. Fry each batch for 5 to 10 seconds and transfer to a paper towel to drain.

6. Remove the beans from the oven and top with the fried onions. Return to oven for 5 minutes. Keep warm until ready to serve.