If you don't have pre-cooked/ leftover chicken get that cooked first. I had bone-in, skin-on chicken thighs that I roasted.
In a large pot on medium heat melt butter and sauté the chopped onion until just soft and slightly translucent.
Add broth, carrots, bay leaf and cooked chicken, I left the thighs whole to get as much flavour as possible. Simmer for 20 minutes.
At this point I pulled out the whole chicken thighs.
Add the mushrooms and celery, cover and simmer for 15 minutes.
While this simmers, I pulled the meat from the thighs and discarded the skin and bones. Mix the meat back into the broth.
Mix the water and flour together to make a slurry, ensure there are no lumps and it's completely smooth.
While stirring constantly, slowly mix the flour slurry into the broth. Let the mixture bubble for 3 minutes.
Stir in the cream and let cook until thickened.
Add in your seasoning and green peas, let simmer for a minute or two.