Preheat a wood-fired pizza oven to very hot 4 hours before cooking.
Bring a large pot of salted water to a boil. Add the mustard greens and cook about 3 minutes. Drain and rinse with cold water. Chop into large pieces.
Sprinkle some flour on your pizza peel. Using a rolling pin, stretch your dough to a very thin 10-inch round.
Drizzle some extra-virgin olive oil on each round, leaving a 1-inch crust. Sprinkle with a quarter of the mozzarella and a handful of fontina.
Gently put the pizza on the floor of the pizza oven. Bake until the cheese is just melted, 2 to 3 minutes. Remove the pizza and top with a quarter of the greens and a quarter of the slices of speck. Place back in the oven and bake for another minute. Remove the pizza and drizzle with olive oil. Slice and serve immediately.
Repeat with the remaining 3 balls of pizza dough.
Cook's Note: Alternatively, you can use a preheated pizza stone in your home oven. It's best to heat it for 1 hour at 500 degrees before baking.
In the bowl of a stand mixer, stir the yeast, lukewarm water and 1/2 cup bread flour. Mix well and let sit until bubbly, about 30 minutes.
Whisk together the remaining 3 1/2 cups bread flour and salt in another bowl.
Once the yeast mixture is nice and bubbly and looks like foamy beer, add the cold water and olive oil. Using a dough hook, turn the mixer on and add the flour in increments. Mix the dough until the dough starts creeping up the dough hook and comes away from the sides of the bowl, about 5 minutes.
Place the dough in a large bowl lightly greased with olive oil. Turn to coat all sides with oil. Cover the bowl loosely with a tea towel. Let rise until doubled in size, about 2 hours. Punch the dough down, and let rise another hour.
Divide the dough into 4 equal disks.