In a large skillet, heat 1 tablespoon of olive oil and sauté the onions for 10 minutes until they begin to brown. Add the mushrooms and sauté 5 minutes, then add the leeks, 2 tablespoons each of minced garlic and chopped rosemary and sauté 3 minutes more. Place the pizza crust on a baking tray, brush the entire top of the crust with half of the olive oil mixture, and then top with the mushroom and onion mixture. Arrange the sliced olives and artichoke hearts on top. Reduce the oven temperature to 425˚F., place the pizza on a center rack in the oven and bake 12 minutes or until the crust is browned on the edges. Remove from the oven and drizzle or brush the remaining olive oil mixture over the pizza, sprinkle with black pepper and serve.