Preheat the oven to 190°C.
In a medium pot, melt the butter over low heat. Add the finely chopped shallot and fry until translucent. Then, add the wheat flour and stir with a whisk for 2-3 minutes.
Remove from the heat, pour in the broth and stir vigorously with a kitchen whisk until a thick sauce is obtained. Add the remaining sauce ingredients: the wholegrain mustard, Dijon mustard, honey, cream and thyme/tarragon. Mix thoroughly and set aside.
Cut the chicken breast into 2-3 cm thick slices and arrange them in a large ovenproof dish, ensuring they don’t overlap. Spread the prepared mustard sauce evenly over the chicken.
Place the prepared chicken in the preheated oven and bake for approximately 20-24 minutes or until the chicken is cooked through. It's a good idea to check the meat after 20 minutes and, if needed, continue baking for a few more minutes.
After baking, give the sauce a gentle stir to achieve a smooth consistency.
Serve with your favourite side dish. Enjoy your meal!