Melt the remaining 1 tablespoon of butter in the skillet. Add the cremini mushrooms, season with salt and pepper and cook over moderate heat until browned, about 5 minutes. Add the morels and cook, stirring, until they start to darken, about 3 minutes. Add the wine and simmer over moderately high heat until reduced to 3 tablespoons, about 3 minutes. Add the stock and slowly pour in the reserved morel soaking liquid, stopping before you reach the grit at the bottom. Simmer until reduced by two-thirds, about 6 minutes. Add the cream and tarragon and simmer until thickened, about 4 minutes. Add the lemon juice and season the sauce with salt and pepper. Add the chicken breasts to the skillet, skin side up, along with any accumulated juices, and simmer over low heat until the chicken is hot, about 3 minutes. Transfer the chicken breasts to plates and serve with the sauce.