Season the guinea fowl supremes with salt and pepper. Melt the butter in a frying pan over a low to medium heat, then add the guinea fowl, skin side down. Cook over a low to medium heat to render the fat beneath the skin. This will help to caramelise and crisp the skin. Once the fat is rendered and the skin browned, turn the guinea fowl over, reduce the heat and continue to cook until the supremes are cooked through, about 10 minutes. Remove the guinea fowl to a warmed plate and leave to rest in a warm place while you finish the sauce. Pour off the excess fat from the pan and deglaze with the wine. Reduce to 1–2 tablespoons. Add the stock and reduce by half. Stir in the cream and simmer for 2–3 minutes. Coarsely chop enough tarragon leaves to give you 1 teaspoon, and add to the sauce. Taste and season with salt and pepper, then serve.