Pat the chicken thighs dry with paper kitchen towels. Using a sharp knife, lightly score the thicker parts of each thigh for even cooking. Season both sides with salt and pepper. Leave to rest 20 minutes skin side up. Pat dry again using paper towel just before cooking. Stretch the skin to cover all the meat. Using a sharp point paring knife, prick a few holes in the skin.

in a large pan over medium high heat, add 3-4 tbsp of olive oil. Place the chicken thighs in the skillet, skin side down. Place parchment paper on top to cover them, ideally in the form of a round cartouche. Place a weight on top of the paper to help flatten the thighs. Cook for about 5-7 minutes, or until the skin is crispy and golden brown. Avoid moving them too much, so the skin can get really crispy. Remove weight and paper then flip the thighs and cook for another 3-4 minutes on the other side. Remove the chicken from the pan and set aside on a hot plate, in warm spot.

For the sauce, in the same pan, add the chopped shallot and sauté until translucent, about 2 minutes. Add the grated garlic, cook 30 seconds. Stir in the tomato paste and cook for 1 minute while stirring over low heat. Deglaze with the red wine, scraping up any brow bits from the bottom of the pan. Reduce by half then add in the vinegar. Add the tarragon herb. Bring to a simmer and cook for about 5 minutes to reduce slightly.

Pour in the chicken stock and bring to a boil. Reduce the heat and let it simmer until the sauce reduces by half or starting to look thicker, about 10 minutes. Once reduced, add salt and pepper to taste. (Taste it)

Stir in the butter a little at a time as you mix well over very low heat. It will emulsify into a thickened glossy sauce. Do not boil or it will separate.

You can return the chicken thighs to the skillet, skin side up, to reheat them 30 seconds. Otherwise place them under the broiler to reheat them keeping that skin crisp. Add the sauce to your serving plate first, and the chicken on top.