Preheat oven to 200C/390F. Pat the tenderloins dry then season all over with salt & pepper.
Add a drizzle of oil in a large cast-iron or oven-safe pan over medium-high heat. Sear the tenderloins until golden all over, approx 4-5 minutes.
Transfer the pan to the oven & roast for 11-14mins, or until the thickest part reads 63C/145F. This will leave the pork with a blush of pink*. Place the pan back on the stove then transfer the tenderloins to a plate to one side.
Turn heat to medium & add shallots to the leftover fat. Fry until they soften & soak in all the flavour in the pan (they'll turn dark, just be careful they don't burn). Pour in stock then stir in Boursin until it blends into a sauce. Gently simmer for a few mins, or until the sauce begins to thicken. Stir in the resting juices from the pork, then simmer for another minute or so until it re-thickens. Slice the pork (I like around ¾" portions) then drizzle over sauce & enjoy!