Cook the bacon or guanciale in the oven until golden and crispy. Drain on paper towel and set aside. Be sure to reserve the rendered fat for later.
Once cooled, break the bacon up into smaller pieces or cut the guanciale into small pieces. Place a large stock pot filled with the vegetable stock to boil, if unsalted, add some salt to taste.
When it comes to a boil, add the capellini and carefully stir until all are in the stock and covered. Allow them to cook, stirring so as not to stick until cooked to your taste (al dente is best.)
Remove the cooked capellini and place them in a large sauce pan on the stove top; put the heat on medium-low. Reserve the cooking stock (do not discard.)
Add a healthy drizzle of the rendered cooking fat from the bacon or guan
Now add the cooked bacon or guanciale, a good amount of grated parmigiano-reggiano cheese and a small scoop of the vegetable cooking stock (do not add too much at one time) and carefully stir and mix well over low to medium heat until a sauce forms and coats the strands of pasta.
You need to add more stock if needed, but once all is completely blended be sure to remove from the heat and add plenty of chopped parsley and cracked black pepper.