Place an oven rack in the center of the oven. Preheat the oven to 450 degrees F. Spray a baking sheet, liberally, with vegetable cooking spray. Set aside
Lay the potatoes and zucchini on 2 kitchen towels. Bring the corners of the towels together and squeeze out the moisture from the vegetables. Place the vegetables in a large bowl. Add the garlic, chopped rosemary, 1/4 cup Parmesan cheese, bread crumbs, egg whites, salt, and pepper. Mix well until all ingredients are combined.
In a 12-inch nonstick skillet, heat the vegetable oil over medium heat. Add the vegetable mixture to the pan. Using a spatula, press the mixture evenly into the pan. Drizzle the top with olive oil and sprinkle with the remaining 1 tablespoon Parmesan cheese. Cook for 8 minutes or until the edges of the mixture begin to brown. Slide the pancake, cooked side down, onto the prepared baking sheet. Bake for 20 to 25 minutes or until the top of the pancake starts to brown and the edges are crispy.
In a small bowl, beat the mascarpone until smooth and season with salt and pepper, to taste.
Cut the pancake into 1 1/2-inch squares and arrange on a serving platter. Pipe or spoon the seasoned mascarpone on top and garnish with a few fresh rosemary leaves.