sauteed lamb medallions with red wine and fresh mint

1 1/2 lb saddle of lamb boned,split, with loins barded and(1 1/2 to 2 lbs.) and aprons
1 md onion
1 md carrot
2 cloves garlic
1 leek
3 t vegetable oil
1/2 c loosely fresh mint,packed leaves
1/2 t thyme,dried
1 bay leaf
2 c fresh lamb (or beef stock) or beef broth,canned
1 1/2 c red bordeaux wine such as merlot (or cabernet)
2 t butter,chilled

preparation:
trim the apron meat of all fat and set aside. peel the onion, carrot, and garlic. coars