Heat the oil in a shallow casserole or frying pan and brown the chicken breasts. This should take 2 minutes per side on a medium-high heat. Remove to a plate.
Add the chopped garlic and thyme to the pan (and if you have an open bottle of white wine, a little splash will help deglaze it). Cook on a medium heat for 2 minutes.
Pour in the chicken stock and spoon in the crème fraiche and wholegrain mustard. Whisk until the sauce comes together.
Add the Parmesan and stir until it has melted into the sauce.
Place the chicken breasts back into the sauce with the baby spinach. Simmer on a low-medium heat for 10-15 minutes, until the chicken breasts are cooked through (it will depend on the size of your chicken breasts to how long this will take). To test the chicken, slice into the middle of one breasts and make sure there is no pink colour remaining.
Season and serve with the freshly chopped parsley,
