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).
Cook the asparagus in a medium-sized saucepan of boiling, salted water for 3 minutes or until tender crisp. Drain and set aside in a medium-sized bowl.
Meanwhile, melt the butter and olive oil in a medium-sized frying pan over medium heat. Add the leek and cook, stirring, for 3 minutes or until soft and lightly browned, then transfer to the bowl with asparagus.
Use a fork to whisk the eggs, Parmigiano Reggiano and parsley in a medium-sized bowl. Season well with salt and pepper. Arrange half of the asparagus and leeks on the base of the baking dish, then scatter the Provolone cheese on top. Add the remaining cooked asparagus and leek on top of the Provolone and drizzle any remaining butter on top. Pour the egg mixture evenly over the asparagus and leek. Bake the frittata for 25 minutes.
Allow the frittata of asparagus and leek to cool for 5 minutes before serving – buon appetito.
2 bunches (300g-400g) asparagus, woody ends trimmed, cut into 4cm lengths|40g unsalted butter, plus extra to grease baking dish|2 tablespoons (40ml) extra virgin olive oil|1 leek (white section only), washed, dried, cut in half lengthways and thinly sliced|6 eggs|30g Parmigiano Reggiano, finely grated|1 tablespoon parsley|150g Provolone cheese, cut into small cubes|Sea salt, freshly ground black pepper