For quickest preparation, heat a splash of olive oil in each of two frying pans over medium-high heat. Sear chicken until golden brown in one frying pan and brown mushrooms in the other. Alternately, using only one frying pan, sear the chicken first, then brown the mushrooms while the chicken is in the oven.
Transfer seared chicken to a baking sheet, then place in the preheated oven for 20 minutes.
Meanwhile, in other pan, brown mushrooms. Add onion and cook, stirring, until onion is softened. Add garlic and cook an additional 30 seconds or so. Add wine (or chicken stock) and allow to cook until the alcohol has thoroughly cooked off and most of the liquid has disappeared, about 2 minutes. Stir in flour, then cream, tarragon and lemon juice. Taste and season generously with salt and pepper, as needed. Return chicken to pan with mushroom sauce. Cook chicken in sauce for a few minutes, then serve. Serve over rice or mashed potatoes.
Notes
Be sure to read the "Cook's Notes" in the original post, for more tips, options, substitutions and variations for this recipe!