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).
Heat half of the olive oil in a medium-sized frying pan over medium heat. Add the leek and cook, stirring, for 2 minutes or until soft. Add the potatoes and cook, continuously stirring until the potatoes are golden and tender.
Use a fork to lightly whisk the cream and eggs together in a bowl until combined. Stir in the remaining olive oil, Parmigiano Reggiano and rosemary. Season well with salt and pepper to taste.
Arrange the potato and leek mixture on the base of the baking dish. Pour the egg and cream mixture evenly over the potato and leek. Bake the frittata for 25 minutes.
Allow the frittata ‘di patate’ (of potatoes) to cool for 5 minutes before serving – buon appetito.
4 tablespoons (80ml) extra virgin olive oil|1 leek (white section only), washed, dried, cut in half lengthways and thinly sliced|500g desiree potatoes, peeled, sliced|60ml thickened cream|6 eggs|40g Parmigiano Reggiano, finely grated|Leaves of 2 sprigs rosemary, finely chopped|Butter for greasing baking dish|Sea salt, freshly ground black pepper