In a saut� pan over medium-high heat, add enough oil to lightly coat pan. Salt and pepper the tenderloin on both sides and sear for 3-4 minutes per side until all sides are browned. Transfer to an oven-proof dish and add 1/2 cup of the stock. Bake uncovered 20-25 minutes, until pork is slightly firm to the touch, registering 150° F on a meat thermometer.
While pork is baking, return saut� pan to medium heat and add Cognac to deglaze pan. Add remaining 1 cup stock to pan and reduce by half. Add jam and reduce to sauce consistency. Transfer sauce to a medium bowl.
Remove pork from the oven, and pour the pan juices into the sauce. Let the pork cool while you move on to the next steps. On medium heat, saut� the beet greens until slightly wilted.
Plate greens, top with pork that has been cut into 1/4-1/2 inch slices, and drizzle with sauce.