Heat a large saute pan over medium-high heat. Season pork with salt and pepper to taste. Add coconut oil to pan.
Sauté pork in oil until browned all over, about 2 minutes on each side. Transfer pork to an ovenproof dish and roast in oven for 12 to 13 minutes, until meat thermometer inserted into the thickest part of the tenderloin reads 145 degrees Fahrenheit, followed by a 5-minute rest time.
Meanwhile, return saute pan to stove top over medium heat and add shallot, salt and cracked black pepper. Saute until golden brown, about 2 to 3 minutes.
Add plums and saute until they start to soften and brown.
Add coconut sugar and cook for 1 to 2 minutes, stirring constantly, until sugar is melted and bubbling. Add wine, scraping the bottom of the pan to loosen all the browned bits. Continue cooking, for about 12 minutes, stirring frequently, until liquid is reduced by half and mixture becomes a chunky sauce. Stir in butter and remove from heat.
Remove roasted pork from oven and transfer to a cutting board. Allow to rest for 5 minutes under a foil tent.
Cut pork into 1/2-inch thick diagonal slices and arrange on serving plates. Add any remaining pork juices to the sauce. Spoon sauce over the pork and serve immediately.