1. Peel the potatoes and celeriac and cut into cubes. Heat the oil in a high-sided saucepan and sweat the potato and celeriac with the bay leaf and half the garlic for 2 to 3 minutes. Cover the vegetables with the milk and cook for 8-10min until the potatoes and celeriac are soft. Season with salt and pepper.
2. Meanwhile, finely chop the onion and remaining garlic.
3. Season the chicken breast with salt and pepper and fry in olive oil until golden brown on both sides. Set aside for a moment.
4. In the same pan, fry the finely chopped onion and garlic until the onion is translucent, add the tomato paste and tarragon. Fill with chicken stock, stir and add to the sauce. Add the chicken breast and season with balsamic vinegar, salt and pepper.
5. Let the sauce simmer and after 10 minutes add the cherry tomatoes and capers. Leave to simmer for a further 7 to 8 minutes until the chicken breast is cooked.
6. Meanwhile, drain the potato and celeriac (if necessary) and mash finely with a knob of butter. Season to taste with nutmeg, salt and pepper.
7. Serve the chicken breast in tomato sauce with mashed potato and celeriac and extra tarragon.

Tip: The celeriac can be replaced by turnip/swede or cauliflower.