First, the bacon. Cook it first, either on the stovetop or in the oven. Personally, I cut it into chunks for optimal crunchiness and cook it in the same pot I plan to cook the pasta in. You can cut it into chunks afterwards if you prefer. Remove about half the bacon from the pot and set aside for topping. If you've got a lot of grease, you can drain it, but leave a little for flavor.
Place pasta the large pan/pot and top with the water/broth, chopped sun-dried tomatoes, and minced garlic.
Cover slightly with a lid (I keep mine off-center, but if it isn't covered, it's okay - this dish is very forgiving) and bring to a boil. Reduce to a simmer and cook for about 8 minutes, or until the pasta is al dente and most of the liquid has been absorbed. (If the water is boiling too rapidly, it will evaporate quickly instead of getting absorbed by the pasta. You can just add a little more water and continue cooking.)
Add the cheese and the milk and stir until melted and creamy. Divide pasta amongst serving bowls and top with the remaining bacon! Garnish with walnuts and parsley if desired.