Place chicken in a large glass baking dish, place half chicken, spreading pieces into a flat single layer.
Submerge chicken in water, add ½ cup salt and two heaping tablespoons of black pepper, and one large lemon, sliced and juiced. Refrigerate and allow to brine overnight or throughout the work day.
Drain the chicken and gently pat dry, discarding the brine and lemons.
Preheat oven to 425°. Season chicken generously with salt.
Heat 2 tbsp. oil in a large cast-iron skillet over medium-high. Once skillet is hot, cook chicken, skin side down, until skin is golden brown and well on its way to being crispy (try weighing it down with another heavy skillet or dutch oven for maximum crispiness), 9-11 minutes.
Turn chicken and add potatoes, and onions to the bottom of the pan.
Transfer skillet to oven and cook until chicken reaches 165F, and tiny potatoes are tender, about 15-18 minutes.