1. Preheat an oven to 375°F.

  2. Remove the pie crust from the fridge so it can begin to thaw.

  3. Cook the filling ingredients: Start by sautéing the onion in a large skillet. Then add the mushrooms. Dice the turkey sausage into small pieces, then add it to the pan. Add the thyme, rosemary, salt, and pepper. Turn the heat up and add the frozen spinach. Continue to sauté until the mixture is warmed.

  4. In a large bowl, beat the eggs and the half & half. Add the mustard powder, nutmeg, and salt, and stir.

  5. Deploy the pie crust into the pie pan. Spread the filling into the pie crust, and spread the cheese evenly across the top.

  6. Slowly pour the egg mixture over the filling.

  7. Bake for 55 minutes at 375°F.

  8. Check before removing the quiche from the oven by grabbing one edge of the pan and jiggling it. If the center of the quiche is not almost set, leave it in for longer. (Note that it doesn't have to be completely set since it will continue to cook after you remove it from the oven.)

  9. Let the quiche sit for about 15 minutes before serving.