Heat a large, deep sauté pan (or a large, wide pot) over medium high heat and cook the bacon until browned and crispy. Remove and set aside on paper towel lined plate. Leave as much or as little bacon fat in the pan as you like.
Add onion and garlic and cook in bacon fat until fully softened and lightly browned, about 3-4 minutes.
Pour 1 cup chicken broth into pan, scraping away any browned bits from the bottom of the pot. Then, stir in 1 more cup of broth.
Add milk, peas, pasta, salt and pepper to pan and stir well. Bring to a boil, then reduce heat to a simmer and cook until pasta is done and sauce has thickened, about 10 minutes. While pasta is cooking, add remaining cup of broth as needed to cook pasta and create a thick, creamy sauce.
Once pasta is done, take off the heat and stir in ricotta cheese and grated parmesan. Crumble bacon and stir into dish along with chopped parsley, if using. Serve immediately.
Shells: Feel free to use a different pasta shape, but I do recommend using a smaller shape that cooks in less than 10 minutes. Elbow macaroni work great, as do bow ties.
Chicken broth: Vegetable broth works in a pinch. I do not recommend beef broth, as it can have an overpowering taste.
Milk: I mostly use whole milk for this recipe, although 2% works great, too. 1% is OK. I would not recommend fat free milk, the pasta would be more watery/less rich.
Peas: I have made this pasta with corn in place of the peas, and with a mixture of peas and corn. Works great!
Bacon: Diced ham is a great substitute for the bacon, if you're looking for something a little lighter.
Ricotta: I love ricotta in this recipe, although cream cheese works just as well. Mascarpone yields a very decadent pasta (delicious! but decadent).
Garlic/onion: I really like the combination of bacon, garlic and onion in this recipe, although the original version of this recipe didn't include the onion and garlic. Feel free to leave them out, or to use ¼ teaspoon each onion and garlic powder instead.
Do not pre-cook the pasta! It really does go in completely dry and uncooked. If you pre-cook it, your dish will come out very soupy.
Make sure you only add 2 cups of the chicken broth initially, then gradually add the remaining cup to the pasta as it is cooking. This way, you only add as much as you need (different types of pasta require different amounts of liquid). If the dish seems too dry/not saucy enough once you stir in the ricotta cheese, just add another splash of broth to thin it out a little.
I highly recommend serving the pasta right away - it will continue soaking up liquid as it sits and cools, and it really is the creamiest and tastiest when it is served as soon as it has finished cooking.