Barbara Bush's Mushroom Quiche

Ingredients

• 3 tablespoons unsalted butter
• 1 1/4 pounds mushrooms, sliced
• 3 green onions, minced, plus more, to taste, for garnish
• 1 clove garlic, minced
• 3 shallots, minced
• 1 3/4 teaspoons oregano
• 1 3/4 teaspoons basil
• 1 1/4 teaspoons salt
• 3/4 teaspoon marjoram
• 1/4 teaspoon black pepper
• 1/4 teaspoon thyme
• 1/2 teaspoon dry mustard
• 4 eggs
• 3/4 cup whole milk or half-and-half
• 1 (9-inch) pie crust, unbaked