Preheat the oven to 425°F. Roll out the pie dough and press it into a pie dish; set aside.
In a large mixing bowl, whisk together the eggs and heavy cream or milk until smooth. Add the bacon, spinach, shredded cheese, salt, and pepper, stirring until evenly combined.
Pour the egg mixture into the prepared pie crust. Bake at 425°F for 20 minutes, then reduce the oven temperature to 350°F and continue baking for 30–35 minutes, or until the center is set. If the top begins to brown too quickly, loosely cover with foil.
Remove from the oven and let rest for about 10-15 minutes before slicing and serving.