Step 1Add sugar and yeast to warm water in bowl; stir to dissolve yeast. Add 4 cups flour, 2 teaspoons salt and onion. Knead dough on floured board until smooth, 5 minutes.
Step 2Place dough in oiled bowl and let rise in warm spot until double in bulk, 1 hour. Flatten out dough on oiled cookie sheet to 16x12-inch rectangle about 1-inch thick. Sprinkle with salt and dried rosemary, to taste.
Step 3Bake at 400 degrees until golden and sounds hollow when tapped, 20 to 25 minutes. Serve hot.