Melt butter in a large saucepan over medium heat. Add chopped leeks and cook until softened, then add mushrooms and garlic. Cook another 2-3 minutes until soft.
Whisk arrowroot into bone broth until fully dissolved.
Add kale to the saucepan and gentler stir, these will cook down quickly.
Pour in broth and coconut milk, stir. Whisk in nutritional yeast and mustard and combine.
Raise heat and bring to a boil while stirring until thickened then return heat to low.
Add in chicken, herbs, and salt and pepper. Simmer another few minutes to combine flavors.