Heat the oil in a large non-stick pan set over a low-medium heat and cook the pancetta until the fat renders out and it becomes crispy. 

Push the pancetta to one side and add the leeks. Sauté in the pancetta fat for a few minutes, stirring often, until softened. Remove from the heat, scoop out the leeks into a blender and set aside.

Meanwhile, cook the pasta in boiling salted water with the garlic cloves for a few minutes less than the packet instructions (you will finish cooking it in the sauce later and you want to ensure it is served ‘al dente’). Scoop out a mug of the pasta cooking water, then drain the rest. Set aside.

Add the spinach, peas, Parmesan, basil, and softened garlic (which should be nestled in your drained pasta) to the leeks in the blender with approx. 120ml of the pasta cooking water. Blitz until smooth.

Add the cooked pasta to the pan with the pancetta. Pour in the sauce and toss together really well to combine. 

Return to the heat and cook for a minute or so until heated through and the pasta is perfectly cooked. Turn off the heat and add the whisked egg yolk. Keep tossing until you have a smooth and glossy sauce (you can add more pasta cooking water if you need it). Taste and adjust the seasoning with salt and freshly ground black pepper as needed - Parmesan and pancetta are quite salty, so proceed with caution. 

Spoon into bowls and serve with more freshly grated Parmesan. Enjoy!