1.
Preheat the oven to 180°C.
2.
Add the spinach to a saucepan of boiling water and cook for 3-4 minutes until completely wilted. Drain, rinse under cold water and squeeze out any excess water. Pat spinach dry with paper towel, then finely chop and set aside.
3.
Heat the oil in a large frypan over medium heat. Add the onion and leek, then cook, stirring, for 4-5 minutes or until mixture starts to soften. Add the garlic and cook for a further 1 minute. If necessary, add 1-2 tablespoons water to the pan to prevent the mixture from burning. Add the chopped spinach, then season with sea salt and freshly ground black pepper and stir well to combine.
4.
Divide the leek mixture evenly among 6 individual cast-iron pans or ovenproof quiche dishes. Top with strips of prosciutto, cherry tomatoes and 3/4 cup (90g) peas.
5.
Crack the eggs into a bowl and whisk to combine. Add the sour cream and whisk thoroughly. Add the milk and paprika, then season with a pinch of salt and lots of freshly ground black pepper. Add half the chives and 150g grated pecorino, and mix well.
6.
Carefully pour the egg mixture over the leek filling into the pans or dishes. Scatter with remaining 1/4 cup (30g) peas, chives and 50g pecorino, then season well with freshly ground black pepper.
7.
Bake frittatas for 30 minutes or until egg is set and centre is slightly firm to the touch. Garnish with oregano leaves and extra grated pecorino before serving warm or at room temperature.