Begin by preparing the ingredients. Finely dice the shallot and slice the cremini mushrooms. Mince the garlic and set aside. Gather the sauce ingredients so they are ready to adde when needed. Season the chicken breasts with kosher salt and pepper.
Place a wide skillet over medium high heat. When the pan is hot, add 2 tablespoons of olive oil. Add the chicken breasts and let sear undisturbed until well browned. When the chicken is golden and releases from the pan, flip them over and brown on the other side. When both sides are brown, remove the chicken to a plate and set aside.
Turn the heat down to medium and add the remaining tablespoon of olive oil along with the butter. Add the diced shallots and sauté for 2 to 3 minutes until softened and translucent. Add the sliced mushrooms and sprinkle with a bit of kosher salt. Sauté for about 5 minutes until the mushrooms are tender.
When the mushrooms are fully cooked and beginning to brown on the edges, add the minced garlic. Cook for another minute until the garlic is fragrant. Turn the heat back up to medium high and deglaze the pan with the whiskey. Be careful when adding the whiskey to the hot pan as it can spatter.
Allow the whiskey to simmer until reduced by about half, for a minute or two. Add the chicken broth and the heavy cream. Bring the sauce to a simmer and add the chicken breasts back to the pan along with any juices on the plate.
Turn the heat down to medium low. Cover the skillet if possible and cook the chicken breasts until they reach an internal temp of 165°F / 74°C, about 5 to 8 minutes. When fully cooked remove the chicken to a clean serving platter and tent with foil.
Check the seasoning of the sauce, adding more kosher salt and pepper if needed. In a small bowl or cup, stir together the flour and 4 teaspoons water until a smooth paste. Add the flour mixture to the sauce and quickly stir to combine. Simmer the sauce until it thickens to the desired consistency. If you prefer the sauce thicker, you can add a bit more flour mixed with water.
Finish the sauce with the fresh lemon and chopped fresh parsley. Serve the chicken breasts with the whiskey mushroom cream sauce and enjoy!