In a large heavy-based pot, add bacon strips and fry over low heat until they're well browned and the fat has rendered out (usually about 10 minutes), then remove to a plate (don't wipe out the pan).
150 g bacon
Sprinkle chicken thighs with ¼ teaspoon each of salt and pepper, then add to the same pot and fry (adding olive oil if needed) over medium-high heat until seared on both sides, (not cooked through - we will do this later), then remove to a plate.
½ teaspoon cooking salt (divided), ¼ teaspoon freshly ground black pepper, 400 g chicken thighs, 1 tablespoon olive oil
Turn the stove down to low, add onion, carrot and celery and stir until they start to soften.
1 brown onion, 1 carrot, 1 rib celery
Add garlic and dried herbs and continue to cook for 30 seconds.
3 fresh garlic cloves, ¼ teaspoon dried rosemary, ¼ teaspoon dried thyme, ⅛ teaspoon ground sage
Sprinkle over plain flour and stir to coat the vegetable mixture, then continue to stir over low heat for 2 minutes.
2 tablespoons plain flour (all-purpose flour)
Gradually add stock (in approximately ⅓ cup increments for the first 1½ to 2 cups) and stir each addition until any lumps disappear, before adding the next amount of stock.
4 cups chicken stock
Once all the stock is added, stir in mustard and potatoes, and be sure to scrape up the browned bits from the base of the pan.
1 tablespoon Dijon mustard, 400 g potatoes
Bring to a simmer, partially cover with a lid and simmer for 10 minutes or until the potatoes are tender.
Meanwhile, chop chicken and bacon into bite-sized pieces.
Stir in chicken, bacon, remaining ¼ teaspoon of salt and cream, then simmer over low heat until the chicken is cooked through.
½ cup thickened cream, ½ teaspoon cooking salt (divided)
Stir in cheese until it melts, ladle the soup into bowls and serve garnished with chopped chives (if using).
60 g grated cheddar cheese, finely chopped chives