Prepare the chicken – Season the chicken breasts lightly with salt and pepper. This early seasoning helps flavour the meat all the way through.

Brown the chicken gently – 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 goal is colour, not full cooking at this stage. Remove the chicken and set aside.

Soften the onion – In the same pan, add the chopped onion and cook gently until soft and translucent. Stir regularly and avoid browning, as this keeps the sauce mild and creamy.

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

Pour in the stock – Add the chicken stock gradually, stirring constantly to avoid lumps. Let the sauce come to a gentle simmer until it thickens slightly.

Add cream and tarragon – Stir in the double cream and most of the chopped tarragon. Keep the heat low so the sauce stays smooth and doesn’t split.

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

Finish the sauce – Add a small squeeze of lemon juice and the remaining tarragon. Taste and adjust seasoning if needed.

Rest briefly before serving – Let the dish stand for a couple of minutes off the heat so the sauce settles and thickens slightly.