Clean the leeks: Trim the root end as well as a few inches off the dark green part at the top. Halve the stalk lengthwise and slice into ¼ inch thick half-moons. Place the sliced leeks in a bowl of water and mix them all around, agitating to remove the dirt. Lift out the leeks with your fingers and set aside. (if the water is very dirty, repeat the process once more.)
Cook the pasta according to package instructions.
In a large sauté pan, over low heat, add butter and olive oil and sauté the leeks until soft and translucent.
Add the garlic and crushed red pepper flakes and sauté for 1 minute, stirring often.
Stir in the tomato paste to coat the leeks + garlic.
Add the diced tomatoes and wine and continue to cook until the liquid is reduced to half.
Lower the flame, add the salt and slowly add the cream and lemon zest, simmering gently until volume reduces and the sauce thickens a bit.
Add the Parmesan cheese, adjust seasoning.
Toss the cooked pasta with the sauce and garnish with parsley and additional parmesan