Cut up the lamb into bite-sized pieces
Add butter, onion, garlic, and mushroom to a large pot or skillet. Stir continuously until mushrooms are tender.
Add flour and stir through till four is dissolved and the mixture is sticky.
Add the chicken stock and cream, and stir through.
Temper the sour cream in a separate bowl, then add to the mixture. Along with the Worcestershire sauce, dijon mustard, paprika, dried rosemary, salt, and pepper. And stir until everything is combined.
Add the lamb, stir through and then simmer over low heat for 5 to 6 minutes or until the lamb is warmed through.