To prepare dough, lightly spoon the bread flour into a dry measuring cup, and level with a knife. Combine 1/2 cup bread flour, warm water, 1 teaspoon sugar, and yeast, stirring with a whisk. Let stand 15 minutes.
Lightly spoon 1 1/2 cups all-purpose flour into a dry measuring cup; level with a knife. Combine 1 1/2 cups all-purpose flour, 1/2 cup bread flour, and salt in a large bowl, stirring with a whisk.
Make a well in center of mixture. Add yeast mixture to flour mixture; stir well. Turn dough out onto a lightly floured surface. Knead until smooth and elastic (about 10 minutes); add enough of remaining all-purpose flour, 1 tablespoon at a time, to prevent dough from sticking to hands (dough will feel tacky).
Place dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85º), free from drafts, 45 minutes or until doubled in size. (Gently press two fingers into dough. If indentation remains, the dough has risen enough.) Punch dough down; cover and let rest 20 minutes.
To prepare topping, cook bacon in a large nonstick skillet over medium heat until crisp. Remove bacon from pan, reserving 2 teaspoons drippings. Set bacon aside. Add spinach to drippings in pan; sauté 2 minutes or until wilted. Place spinach in a colander, pressing until barely moist. Add onion and 2 teaspoons sugar to pan; cook 12 minutes or until golden brown, stirring frequently. Remove from heat; cool.
Melt butter in a medium saucepan over medium heat. Add garlic; cook 2 minutes, stirring frequently. Add 3 tablespoons flour and pepper, stirring with a whisk; cook 30 seconds. Gradually add milk, stirring constantly with a whisk. Cook 5 minutes or until thick and bubbly, stirring constantly with a whisk.
Preheat oven to 475º.
Roll dough into a 12-inch circle on a floured surface. Place dough on a (12-inch) pizza pan or baking sheet coated with cooking spray adn sprinkled with cornmeal. Crimp edges of dough with fingers to form a rim. Spread milk mixture evenly over dough; top with spinach and onion.
Bake at 475° for 20 minutes. Sprinkle evenly with bacon and cheese; bake an additional 5 minutes or until golden brown. Cut pizza into 8 wedges.