*(If cooking right away) Preheat your oven to 425 degrees and spray your baking dish with non-stick baking spray, or grease with unsalted butter. Bring a large pot of water to a boil and blanch the green beans for just a few minutes. Then, immediately place the green beans into an ice water bath to stop them from cooking further.

Using a large skillet, heat 1 tablespoon of the olive oil and, after a minute or two, add the shallots and leeks and sauté for about 4 minutes, or until they are beginning to soften and brown. Add the mushrooms and thyme, and season with salt and pepper. Cook the mushrooms for about 3 to 4 minutes.

Slowly pour in the chicken stock (or wine), stirring occasionally until the liquid has evaporated, for about 3 to 4 minutes. Evenly sprinkle the flour over the mushroom mixture and toss to coat. Add the vegetable broth and bring to a simmer, stirring often until the sauce has thickened, about 4 to 5 minutes.

Remove from the heat and add in the blanched green beans and toss to coat, drizzling in the remaining tablespoon of olive oil if needed. Transfer to the prepared baking dish and top with the freshly grated parmesan and fontina cheese.

At this point, if you are making this a day in advance, wrap/cover your baking dish and store in the refrigerator. When ready to bake: remove the casserole from the refrigerator and, using a small bowl, stir together the panko, paprika and nutmeg. Sprinkle the panko mixture evenly over the top of the casserole. Bake for about 35 to 45 minutes, or until golden brown on top. Let cool for at least 10 to 15 minutes before serving. Enjoy!