In a small saucepan, combine the apple cider, salt, bay leaves, garlic and peppercorns
Bring to a boil, stirring constantly until the salt is dissolved
Remove from heat and allow brine to completely cool
Place the tenderloin in a marinade/brine container or a ziplock bag and pour in the cooled brine
Cover and place in fridge overnight
Preheat the oven to 425 degrees F
Remove the pork tenderloin from brine and pat dry with paper towels. Discard brine
Heat a large cast iron skillet (oven-safe skillet) over medium-high heat.
Sear the pork loin on all sides until lightly brown.
Place skillet with pork loin in oven and roast for 15-20 minutes until internal temperature reaches 145 degrees F. Remove from oven and let rest for 5-10 minutes.