2 cups chopped mushrooms 7 eggs 1/2 cup half-and-half 1 1/2 cups chopped broccoli 2/3 cup shredded Cheddar cheese 2 large green onions, chopped 1/2 teaspoon garlic salt 1 1/4 cups quinoa flour 1/3 cup butter at room temperature 2 tablespoons water, or as needed
Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9-inch pie dish with butter. Cook and stir mushrooms in a dry skillet over medium heat until soft and mushrooms have released their liquid, about 10 minutes. Remove from heat. Whisk eggs and half-and-half together in a bowl and stir in broccoli, Cheddar cheese, green onions, garlic salt, and cooked mushrooms. Refrigerate filling.
Mix quinoa flour and butter in a bowl until mixture forms small clumps; stir water into quinoa mixture until dough comes together. If dough is too dry, add more water, 1/2 teaspoon at a time, until dough holds together. Press dough into prepared pie dish to form a crust; pour filling into crust. Bake quiche in the preheated oven until a toothpick inserted into the center comes out clean, about 35 minutes.