Boil pasta until just shy of al dente. While pasta is cooking, prepare sauce.
In a large skillet, cook bacon on medium low heat until it is slightly chewy. Remove from pan. It will crisp up when the pasta bake goes into the oven.
Remove all but 2 tablespoons grease from pan.
Add leek and cook until starting to soften, about 2 minutes.
Add garlic and cook until fragrant, about 30 seconds.
Add half and half and cream, bring to a simmer.
Add parmesan and ricotta, stir until melted and combined.
Add nutmeg and salt and pepper to taste.
Simmer until slightly thickened, about 5 minutes.
Stir in pasta and smooth out the top surface.
Sprinkle mozzarella over the top of the pasta.
Roughly chop bacon and sprinkle evenly over the mozzarella.
Place on middle rack in a preheated oven and bake for 7-10 minutes or until the cheese on top is golden brown and bubbly.
Sprinkle with fresh parsley.
Notes
Pancetta can be substituted for bacon, cook it according to recipe directions as you would the bacon.Only use the white and light green part of the leek. Leeks are easiest to wash after they have been chopped. Chop according to recipe directions, place in colander, and rinse until clean. Otherwise grit can get caught between the layers.