Mix the salt and milk kefir together.
Place the chicken in a ziplock bag or a medium bowl and pour in the brine, ensuring that the chicken is covered.
Allow the chicken to sit in the brine for a minimum of 8 hours, or overnight.
An hour before roasting, remove the chicken from the refrigerator to let it come to room temperature.
Preheat the oven to 425º/218ºC.
While the oven heats, prepare the vegetables–washing, peeling and chopping in large chunks. Arrange them on a parchment-lined baking sheet.
Drizzle the vegetables with olive oil and season with salt and pepper.
Scrape off as much brine as possible from the chicken using only your hands. Arrange the chicken over the vegetables and generously sprinkle with fresh ground pepper.
Roast for 20 minutes. When the timer goes off, rotate the pan and turn down the heat to 400ºF/204ºC.
Bake for an additional 30 minutes. The chicken is done when the juices run clear after poking it with a knife, or when it reads 165ºF/74ºC on a thermometer.