Bring a large pot of salted water to a boil.  

Meanwhile, in a large skillet, heat the olive oil over medium-low heat. Add the leeks and cook, stirring continuously, until golden brown, 20 to 30 minutes. 

Add the heavy cream, grated garlic, lemon zest and lemon juice, season to taste with salt and pepper and heat through. 

Cook the pasta according to the package directions, leaving it al dente as it will continue to cook in the sauce. Drain, reserving some of the cooking water. Transfer the pasta to the sauce and stir until it is completely coated. If the sauce looks too thick, add the cooking water ¼ cup at a time to loosen it up.  

Plate the pasta and garnish with more lemon zest.