Note - Before you start cooking this one, have a read of the short blurb above so you can choose your accompaniment and pop it on at the right time whilst cooking the sauce.
Season the chicken breasts with salt and black pepper. Take a large saucepan or frying pan, spray with 1kal and on a medium/high heat fry the chicken breasts for 2-3 minutes on each side until browned. The chicken doesn’t need to be cooked through at this point, you just want some colour on the meat. Remove the chicken from the pan and pop to one side.
In the same pan, spray again with 1kal and add the leek. Season with salt and black pepper and fry for 3-4 minutes until the leek starts to soften. Add a little water if the pan starts to get dry.
Add the garlic and mushrooms and fry for 2 minutes.
Finally add the plain flour, stir through and fry for another minute.
Next add the white wine, simmer for a few minutes until reduced by half and then add the chicken stock, the mustard and the whole sprig of tarragon. Add the chicken back to the pan. Bring to the boil and then reduce to a simmer.
Simmer for 20 minutes until the liquid is reduced slightly and has started to thicken.
Reduce the heat to low/medium and then add the crème fraiche. Stir through until well combined, simmer for another few minutes and then remove from the heat.
Finally stir through the fresh tarragon. Taste and season with more salt and pepper if required.
Serve with the accompaniment of your choice.