- Make the dough: In a bowl, combine 2 cups flour, warm water, and ⅛ teaspoon yeast. Tightly cover and set aside at room temperature for 12 hours.
- Portion rested dough into 4 equal pieces and place into 4 oiled containers. Cover and refrigerate overnight.
- Bring dough to room temperature by covering with a towel and setting on counter for 1 hour.
- In the bowl of stand mixer fitted with dough hook attachment, combine dough with remaining flour, yeast, 2 cups cold water, and salt. Mix on low speed until combined, then mix for an additional 8 minutes on medium speed. Set aside.
- Make the parsnip puree: Peel parsnips, then boil until tender. Strain, then return parsnips to pot. Add cream, salt, and pepper and bring to a boil for 3 minutes. Using an immersion blender, puree parsnips until mixture is smooth. Set aside.
- Assemble the pizza: Preheat grill or oven fitted with pizza stone to 400 degrees. Turn out dough and roll out into a 10-inch circle, then place on a pizza peel dusted with flour. Oil edges of dough with olive oil, then spread with parsnip puree. Sprinkle with mozzarella, then top with brussels sprouts and pancetta. Season with salt and pepper to taste. Bake or grill until dough is crispy and golden brown, about 8 minutes. Remove, sprinkle with parmesan, and serve.