Cut the chicken into 1” (2 cm) pieces and toss in a bowl with the salt. In a large pot, heat the oil over medium-high and brown the chicken in batches, removing to a bowl or hotel pan once browned.
When the chicken is browned, return it all to the pot and add the bay leaf, potatoes, carrots and water. Cover and bring to a boil, then reduce the heat and simmer for 15-20 minutes, until the vegetables are tender and the chicken is cooked through.
Meanwhile, in a second pot, heat the butter over medium heat. Add the onions or leeks, and celery or celeriac. Stir and cook for 10-15 minutes, until vegetables are tender and beginning to brown.
Whisk the flour into the onions and celery, and cook for a further minute to toast the flour. Remove the onion-celery pot from the heat.
Once the potatoes are ready, stir the onion-celery mixture into the pot with the potatoes and chicken and place the pot over low heat. Stir and cook until the stew thickens, a further 5 to 10 minutes.
