Preheat oven to 425 ºF. Line a pie plate with prepared pie crust and set aside. In a large bowl, whisk together eggs, sour cream, half & half and salt until smooth. Add cauliflower and mushrooms to egg mixture and stir gently to combine. Pour mixture into prepared crust. Place pan in oven on center rack and bake for 10 minutes at 425ºF. Lower the temperature to 350ºF and bake an additional 35-40 minutes until golden brown and center has set. Let cool slightly before serving.