To make the crust: In a large bowl, combine 3 1/2 cups flour, yeast, 2 teaspoons salt and sugar. Create a well in the center of the dry mixture.
Pour 1 1/2 cups lukewarm water and 1 tablespoon olive oil into the well. Stir the mixture together until the dough comes together. Knead the dough with your hands until mixed and smooth. The dough should be soft, but if it is sticky, add a tablespoon at a time of flour.
Form dough into a ball, place in an oiled bowl and cover with a clean towel or plastic wrap. Let rise for an hour at room temperature or refrigerate overnight, and let stand at room temperature for 1 hour before shaping. (Alternatively, combine all the crust ingredients in the bowl of a food processor and pulse several times until the comes together in a ball. No need to knead with your hands. Let rise in the closed food processor bowl for 1 hour.)
Thirty minutes before making the pizza, preheat the oven to 450 degrees and place a pizza stone, tiles or a large baking sheet turned upside down on the lowest rack.
To make the topping: Heat 1 tablespoon oil in a large skillet over medium-high. Add sausage and cook, breaking sausage into small pieces with a wooden spoon, about 5 to 7 minutes, until cooked through. Use a slotted spoon to transfer sausage to a bowl. Drain all but 1 tablespoon of fat from skillet and add the spinach and 1/4 teaspoon salt. Cook over medium heat, stirring, for 1 to 2 minutes, or until wilted. Remove from heat.