Place a baking stone in the oven and preheat to 450°. (The stone should preheat for 45 minutes.)
*Note: If you don’t own a pizza stone, you can use a flat (or upside-down rimmed) baking sheet. A baking sheet or cutting board can also stand in for a pizza peel.
Melt the butter in a large skillet over medium heat. Add the onions and stir to coat. Spread the onions into an even layer and cook, stirring occasionally, for 10 minutes. Sprinkle with salt to taste, reduce the heat to medium-low and cook, stirring occasionally, until the onions are nicely browned, about 45 minutes.
Sprinkle coarse cornmeal onto a pizza peel and place the dough on the peel. Using your hands, stretch the dough into a 14- by 16-inch rectangle, and brush with the oil. Season lightly with salt. Sprinkle the goat cheese, then the blueberries and onions, on the crust. Top with the rosemary, leaving a 1-inch border, and drizzle the entire pizza with honey.
Slide the pizza onto the baking stone and bake until the edge of the crust is slightly crisp and lightly browned, about 20 to 25 minutes. Drizzle with olive oil, if desired, and serve.