Preheat the oven to 400°F Grease a 7 1/2 cup shallow, oval baking dish.
Heat the oil in a large shallow pan. Add the garlic and pumpkin and cook, stirring often, to prevent sticking, for 15-20 minutes or until the pumpkin is tender. Meanwhile, cook the potatoes in boiling salted water for 20 minutes until tender. Drain, leave until cool enough to handle, then peel off the skins. Place the potatoes and the pumpkin in a large bowl and mash well with the butter.
Mash the ricotta with a fork until smooth and add to the potato mixture, mixing well.
Stir in the Parmesan. nutmeg and plenty of seasonings into the the potato mixture-it should be smooth and creamy.
Add the egg yolks, one at a time until mixed throughly.
Whisk the egg whites with an electric mixer until they form stiff peaks, then fold gently into the potato mixture.
Spoon into the prepared baking dish and bake for 30 minutes until golden and firm.
Serve hot, garnished with the fresh chopped parsley.