Take the chicken out of the fridge 15 minutes earlier. Pat dry with paper towels.
In a frying pan add 1-2 tablespoons of oil and when hot but not smoking, turn heat to medium and add the chicken pieces and allow to turn golden before turning over. Season with plenty of salt and pepper. Once evenly fried, turn heating down and allow to cook fully till juices run clear. Once chicken is cooked, take the pieces out on a platter.
To cook the sauce, use the same frying pan that you cooked the chicken pieces in. There should be yummy crispy chickeny bits.
In a bowl, add your flour, salt and pepper and slowly add the milk whilst mixing with a hand whisk to a slurry, Try to avoid lumps.
Optional - Mushrooms: Cram in a good helping of mushrooms for some plant goodness. Return the pan to medium-high with a splash of oil; sauté sliced mushrooms with a pinch of salt until their liquid evaporates and edges are golden. Remove to a plate.
Lower the heat and pour the milk mixture into the same pan. Whisk gently until thick and gently bubbling (about 5 minutes).
Take it off the boil, add the sour cream and mix until combined. Taste and adjust seasoning if needed, and add a small squeeze of lemon if you like.
Return chicken (and any juices) and mushrooms (if using) to the pan and warm through on low heat. Scatter herbs and serve immediately with freshly ground black pepper and a squeeze of lemon.
