To make buttermilk, add lemon juice to milk and stir. Let sit for 15 minutes.
In a large bowl, pour buttermilk over chicken. Cover with plastic wrap, and place in the fridge to marinate for 30 minutes to 24 hours.
Preheat oven to 350 degrees.
In a cast-iron skillet over medium heat, add vegetable oil. Take chicken out of fridge and remove from buttermilk. Sprinkle with salt, then dredge in flour. Carefully place chicken in hot oil and brown well on both sides. Add cubed potatoes to the pan and toss in oil. Transfer skillet to oven and bake for 30 minutes. Allow cooling slightly before serving.