• Heat oven to 475º
• Make the topping; combine the onions, flour, panko and salt in a large bowl and toss to combine. 
• Coat a half sheet pan with nonstick cooking spray and evenly spread the onions in the pan. 
• Bake on the middle rack of the oven until golden brown, approx.. 30 min., tossing the onions 2 or 3 times during cooking.  Set aside until ready to use.
• Turn oven temp down to 400.

Beans & Sauce

• While the onions are cooking, make the beans and sauce:
• Bring 1 gallon water and 2 Tbsp salt to a boil in an 8 quart saucepan. 
• Add the beans and blanch for 5 min. 
• Drain in a colander and immediately plunge beans into a large bowl of ice water to stop the cooking.  Drain and set aside.
• Melt the butter in a 12” cast-iron skillet set over medium-high heat. 
• Add the mushrooms, salt and pepper and cook, stirring occasionally, until the mushrooms begin to release some of their liquid, 4 to 5 min. 
• Add the nutmeg and garlic and cook for 1 min. 
• Add the broth and simmer for 1min. 
• Decrease the heat to med-low and add the half and half. 
• Cook, stirring occasionally, until the mixture thickens, 6-8 min.
• Remove from the heat and stir in one-quarter of the onions and all of the beans.. 
• Top with the remaining onions,
• Bake until bubbly, approx.. 15 min. 
• Serve immediately.