Heat oil and 1 tbsp butter in a cast-iron casserole. Sear the chicken pieces over a high flame till they take on a light brown, keep aside.
In the same casserole, saute the cauliflower florets and shallots for 3-4 mins till they catch just a speck of brown. Keep aside.
Add 2 tbsp of butter to the casserole, add the peppercorns and saute for a minute or two. Switch off the flame.
Return the chicken, cauliflower florets and shallots to the casserole.
Now add the carrots, french beans, mushrooms and sausages. Sprinkle in the salt, black pepper powder and thyme.
Pour the white wine and 100 ml warm water, cover the casserole and transfer it to the pre-heated oven. Cook for 35 minutes till the chicken is tender.
Heat a pan over a low flame, add 1 tbsp of butter and the flour, stir continuously until the butter has melted. Cook for 1 -2 minutes. Now whisk in the milk gently using a balloon whisker or a wooden spatula.
Bring to a simmer, sprinkle in the salt and black pepper, stir continuously to ensure that there are no lumps and the sauce is not sticking to the bottom of the pan.
Cook for 3–4 minutes until the sauce has thickened. Keep aside. Allow to cool to room temperature.
Now add the whipped cream to the sauce, stir well to mix.
Carefully remove the casserole from the oven. Uncover and pour the sauce gently over the chicken and vegetables.
Return the casserole to the gas stove, bring to a simmer over a medium flame and continue to cook for a further 5-7 min till the sauce has thickened.
Adjust seasonings. Add more black pepper if you like the heat. Serve hot.