Heat the butter and 1 tablespoon of the olive oil in a large frying pan over a medium-high heat. Season the chicken generously with salt and pepper and cook until golden brown on both sides and the juices run clear (about 6 to 7 minutes each side).

Transfer the chicken to a plate and pour off the fat from the pan, retaining the pan residues. Return the pan to the heat and add the remaining 1 tablespoon olive oil. Add the shallots and garlic and sauté gently until soft, about 2 minutes. Add the wine, stirring and lifting any brown bits on the bottom of the pan. Bring the wine to a simmer and cook until the liquid is reduced by about half, about 3 minutes. Whisk in the stock, cream and mustard and reduce the heat to a gentle simmer. Cook for about 4 to 5 minutes, stirring occasionally, until the sauce has thickened. Stir in the chopped tarragon and taste for seasoning.

Return the chicken to the pan and heat until warmed through. Sprinkle with tarragon leaves and serve immediately with shoestring potatoes, steamed greens and a glass of Wolf Blass White Label Piccadilly Valley Chardonnay.