Season the chicken – Lightly season both sides of the chicken breasts with salt and pepper. This helps flavour the meat from the start.

Brown the chicken – Heat the butter and olive oil together in a large pan over medium heat. Add the chicken and cook until lightly golden on both sides. The chicken does not need to be cooked through at this stage. Remove and set aside.

Soften the onion – Add the chopped onion to the same pan and cook gently until soft and translucent. Stir regularly and avoid browning to keep the sauce mild.

Add the flour – Sprinkle the flour over the onions and stir well. Cook for about a minute to remove the raw flour taste and form the base of the sauce.

Pour in the stock – Add the chicken stock gradually, stirring constantly to keep the sauce smooth. Let it simmer gently until slightly thickened.

Stir in cream and mustard – Lower the heat and add the double cream, Dijon mustard, and wholegrain mustard. Stir gently until fully combined and glossy.

Return the chicken – Place the chicken back into the pan, spooning the sauce over it. Cover and simmer gently until the chicken is cooked through and tender.

Finish and rest – Taste and adjust seasoning if needed. Let the dish rest for a couple of minutes off the heat so the sauce settles before serving.