In a sauté pan over medium-high heat, add enough oil to lightly coat pan. Salt and pepper the tenderloin and then sear 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 degrees F. on a meat thermometer.
While pork is baking, return sauté 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 bowl.
Remove pork from the oven, and pour the pan juices into the sauce. On medium heat, sauté 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.