Heat a large Dutch oven over medium heat and cook the pieces of bacon until all the fat is rendered and the bacon is crisp. Remove from the pot with a slotted spoon to a paper towel-lined bowl and set aside. There should be about 4 tbsp of bacon fat left in the pot... Use this to saute the vegetables (yum!), OR drain it and use a lighter oil (canola or olive). Add the onions, celery, carrots and garlic to the pot (salt and pepper if desired) and saute until very soft but do not let brown. Stir often!! This can take a while depending on the size of your pot, but be patient... the flavour of the soup depends on this step. Add the pureed and canned tomatoes, parsley, thyme and bay leaf. Simmer for about 20 minutes, uncovered. Meanwhile, melt the butter and stir in the flour to make a paste. Stir the paste into the simmering soup and continue stirring until it starts to thicken. Add the chicken stock and stir. Allow the soup to simmer for at least 15 minutes, covered with a lid. Remove the bay leaf and use an immersion blender to puree the soup to a very smooth consistency. If using, add the Parmesan cheese rind to the soup and turn the heat down very low. After about 10-15 minutes the rind should be soft and may even have some cheese melting off. This adds a nice flavour to the soup. Remove the rind and discard. Adjust the seasoning if necessary. Ladle into bowls and serve with the bacon crumbles. Croutons are great with it too! This can also be frozen (cool completely first).