Heat the oven to 220C/200C fan/gas 7, then heat 2 tbsp oil in a large, deep, ovenproof frying pan over medium heat and cook the leeks with a pinch each of salt and pepper for 10-12 mins until softened. Add the peas and cook for 1-2 mins more, then stir through the ham, nutmeg, crème fraîche and mustard. Reduce the heat to medium-low and stir well. Once the crème fraîche sauce has loosened, stir in the gnocchi and most of the cheese. Season to taste.

Combine the rest of the cheese with the breadcrumbs and remaining 1/2 tbsp oil, then scatter this over the gnocchi. Transfer the pan to the oven and bake for 20-25 mins until bubbling and golden. Season with a crack of black pepper to serve.