Preparation & Preheat : Position a rack in the center of your oven and preheat to 375°F (190°C). Trim the stem ends from the green beans. Finely dice the shallot and slice the mushrooms. In a small bowl, combine the crushed pork rinds and grated Parmesan for the topping.
Sauté Aromatics : Place the cast-iron skillet over medium-high heat and melt the butter. Once it foams, add the diced shallot and sliced shiitake mushrooms. Cook, stirring occasionally, for 6-7 minutes, until the mushrooms have released their moisture and are beginning to brown.
Build the Cream Sauce : Pour the vegetable broth into the skillet to deglaze, scraping up any browned bits from the bottom of the pan. Allow the broth to reduce by about half. Lower the heat to medium, stir in the heavy cream, salt, pepper, and a pinch of nutmeg. Let the sauce gently bubble and thicken for about 5 minutes, stirring periodically.
Combine & Transfer : Remove the skillet from the heat. Add the fresh, raw green beans to the cream sauce in the pan, tossing with the spatula until every bean is well-coated. Carefully transfer the entire mixture into the casserole dish and spread evenly.
First Bake : Sprinkle the shredded Gruyère cheese evenly over the top of the green beans. Place the dish in the preheated oven and bake for 25 minutes, or until the sauce is bubbling around the edges and the cheese is fully melted.
Final Crisp : Remove the casserole from the oven. Evenly distribute the pork rind and Parmesan mixture over the melted cheese. Return the dish to the oven and bake for an additional 7-10 minutes, until the topping is a deep golden brown and crisp. Let stand for 5 minutes before serving.
