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).
Place the cauliflower in a small saucepan with cold water. Bring to the boil over high heat, uncovered, then cook for a further 3-5 minutes or until tender. Drain the cauliflower. Refresh under cold water and set aside to cool slightly.
Meanwhile, melt the butter in a medium-sized frying pan over medium heat. Add the olive oil, red onion and pancetta. Cook for 4 minutes or until the onion is soft and pancetta is golden. Stir the cauliflower into the onion and pancetta mixture.
Use a fork to lightly whisk the eggs in a bowl. Stir in the rosemary and Parmigiano Reggiano and whisk until well combined.
Arrange half of the cauliflower and pancetta mixture on the base of the baking dish then scatter over half of the Provolone cheese. Arrange the remaining cauliflower and pancetta mixture and a final scattering of Provolone cheese on top. Pour the herbed egg mixture evenly over the cauliflower and pancetta mixture. Bake the frittata for 25 minutes.
Allow the Baked frittata with cauliflower and pancetta cool for 5 minutes before serving – buon appetito.