• Preheat your oven to 350°F (or 180°C).

  Grease a 2 to 3-quart oven-safe casserole dish with olive oil spray or use unsalted butter.

BLANCH THE GREEN BEANS:

• Trim the stems off of the green beans and discard. Fill a deep sided sauté pan or skillet with water and bring to a boil. Once boiling, add the green beans and a palmful of sea salt. Stir and submerge the green beans, bring the water back to a boil. Once boiling, set a timer for 6 minutes.

  After 6 minutes, use tongs to remove the beans from the boiling water and transfer to a bowl of ice water, submerge the beans. This will lock in that bright green color. Once the beans have cooled, remove and pat dry between kitchen towels. Then transfer to a cutting board and cut the green beans into thirds or half if small.

MAKE THE CASSEROLE:

• In a 10-inch skillet, add (6 tablespoons) the butter and diced onion. Stir and cook about 8 minutes or until the onions are soft and translucent. Add in mushrooms, stir and cook 4 minutes. Next add in the garlic and cook for 1 minute.
• Sprinkle with flour, stir and cook 2 minutes. Then, while stirring, pour in 2 tablespoons dry white wine and 2 cups half and half. Bring to a simmer a stir until thickened to a creamy soup consistency. Remove off of the heat and add in parmesan, kosher salt, lots of freshly ground black pepper and the nutmeg. Stir to incorporate and taste and add more salt if needed.
• Lastly add in the cut blanched green beans and toss into the creamy sauce. Transfer the casserole mixture to the prepared dish and spread evenly. Cover the dish with aluminum foil and bake on the middle rack of your preheated oven for 20 minutes. Meanwhile make the fried shallots.

MAKE THE FRIED SHALLOT TOPPING:

• Melt (3 tablespoons) butter in an 8-inch skillet. Add the thinly sliced shallot with a pinch of kosher salt and heat over medium to medium-low. Toss the shallots in the butter, stirring often until just slightly crispy this make take about 10 minutes.

  Keep in mind that they will crisp up more in the oven.
• Once the 20 minutes are up, carefully remove the casserole and discard the foil. Sprinkle the slightly crispy shallots over top and return the casserole back to the oven for 15 to 20 minutes more, or until the shallots are deeply golden and the casserole is bubbling with lightly browned edges.
• Allow the casserole to rest for 10 minutes before serving.