Preparing the Pork Tenderloin:Preheat oven to 400°F (200°C).Pat the pork tenderloin dry and season generously with salt and pepper.Heat olive oil and butter in an oven-safe skillet over medium-high heat.Sear the pork on all sides until golden brown, about 2–3 minutes per side.Transfer the skillet to the preheated oven and roast for 12–15 minutes, or until the internal temperature reaches 145°F (63°C).Remove pork from the oven and let it rest for 5–10 minutes before slicing.
Making the Apple Cider Reduction Sauce:While the pork is resting, pour apple cider into the same skillet used for pork.Add apple cider vinegar, Dijon mustard, thyme, and honey (if using).Bring to a simmer over medium heat, scraping up browned bits from the skillet.Reduce the cider by half, about 5–7 minutes, until it thickens slightly.Remove from heat and whisk in cold butter to add richness and a glossy finish.Taste and adjust seasoning with salt and pepper.