Trim the tops and ends of your green beans, then cut in half. Bring a pan of salted water to a boil, and prepare an ice bath nearby. Blanch the beans in the boiling water for 2 minutes, then drain and add the beans to the ice bath.

Grease your cast iron skillet with ⅓ of the butter.

On the stovetop, melt the rest of the butter. Add the sliced shallots and cook on medium heat until soft and translucent (roughly 5 minutes). Season with salt and garlic powder, add the mushrooms to the pan and cook for 5 minutes, until soft and reduced in size. Season with pepper and nutmeg. Reduce the heat to medium low and add the chicken stock and cream. Reduce over a gentle simmer for 10 minutes, or until the sauce begins to thicken, then stir in the grated Parmigiano-Reggiano.

Remove the pan from the heat and pour in the green beans and half the crispy onions. Stir thoroughly to combine. Pour the mixture into your greased skillet and cover with aluminium foil. At this stage, you can leave the pan and remaining ingredients in the fridge overnight until you’re ready to cook (up to 24 hours), or cook right away.

When you’re ready to cook the casserole, fire up your Ooni pizza oven. Aim for 500˚F (260˚C) on the stone baking board inside. Check the temperature accurately using the infrared thermometer.

Place the covered pan in the corner farthest from the flames. Cook for 20 minutes, turning the pan every 5 minutes. After 20 minutes, remove the foil and top the casserole with the remaining crispy onions. Return the pan to the oven and cook uncovered for up to 3 minutes, or until the top is golden brown and crisp.

Remove the pan and serve right away alongside the rest of your festive feast.