Fry leeks in butter and oil with a splash of water and bouillon powder for 10 minutes.
Stir in flageolet beans and cook for 2 minutes until heated through and leeks are tender.
Season pork medallions with salt and pepper and brown in butter and oil for 3 minutes per side.
Deglaze the frying pan with Calvados and apple juice, scraping the bottom with a wooden spoon.
Boil the liquid for 1 minute, then stir in sage, mustard, garlic, and cream.
Return the pork to the pan and cook in the sauce for 3 minutes until fully cooked.
Serve pork over the leeks and beans, spoon over the sauce, and garnish with sage.