Ultimate Green Bean Casserole

Ingredients

• 1 cup whole buttermilk
• 1 large yellow onion, thinly sliced into rings (SEE NOTE)
• 1 1/2 cups self-rising flour (SEE NOTE)
• 2 teaspoons fine sea salt
• Vegetable or canola oil for frying
• 1 1/2 pounds fresh green beans, ends trimmed (SEE NOTE)
• 2 tablespoons butter
• 2 tablespoons olive oil, plus more if needed
• 1/2 teaspoon crushed red pepper flakes
• 1/2 teaspoon herbs de provence
• 5 ounces shiitake mushrooms, sliced (SEE NOTE)
• 4 ounces maitake (hen of the woods) mushrooms, torn into pieces (SEE NOTE)
• 3 cloves garlic, minced
• 2 teaspoons fresh thyme leaves
• 1/2 teaspoon fresh rosemary, finely chopped
• 1/4 cup balsamic vinegar
• 1 teaspoon worcestershire sauce
• 1/3 cup all-purpose flour
• 1 3/4 cups chicken stock or broth
• 2 cups half and half
• 2 tablespoons dried mushroom powder (optional)
• 1/2 teaspoon onion powder
• 1/2 teaspoon garlic powder
• 1/8 – 1/4 teaspoon cayenne powder
• 1/2 teaspoon smoked paprika
• Pinch of freshly ground nutmeg
• Zest of one lemon
• 1/2 cup parmigiano reggiano cheese, finely grated
• Kosher salt and black pepper, to taste