Preheat the oven to 180°C conventional oven/ 160°C fan-forced (350° Fahrenheit/Gas 4). Grease a round baking dish with butter (alternatively, line a baking dish with baking paper).
Melt the butter in a medium-sized frying pan over medium heat. Add the olive oil, red onion, rosemary and thyme leaves. Cook, stirring, for 2 minutes or until the onion is soft. Add the potatoes and pumpkin. Cook, continuously stirring until the potatoes are tender (approximately 10-15 minutes). Allow to cool slightly, then use a stainless-steel mashing plate to lightly squash the pumpkin
Use a fork to lightly whisk the eggs in a bowl until combined. Stir in any juices from the frying pan and the Parmigiano Reggiano. Season well with salt and pepper to taste.
Arrange half of the baby spinach on the base of the baking dish, then place the red onion, potato and mashed pumpkin on top of the baby spinach. Pour half of the egg mixture evenly over the vegetables. Arrange the remaining baby spinach and evenly pour over the remaining egg mixture. Bake the frittata for 25 minutes.
Allow the Frittata of creamed pumpkin, potato and baby spinach to cool for 5 minutes before serving – buon appetito.