Preheat oven to 350 F. Butter a DEEP 9-inch pie pan. Set aside.
Place half of the butter in a large skillet over low heat & sauté leek, onion & mushrooms for 5 minutes or until softened. Transfer to a plate & set aside.
Add olive oil to pan, increase heat to high. When oil is hot, add beef & brown. Transfer to a separate plate. Add garlic & barley to pan, season with salt & pepper & cook for 1 minute then return beef to pan & stir to combine.
Place half the potatoes in base of pie pan. Layer meat over top followed by leek mixture. Use back of a spoon to flatten contents of pie, the overlap remaining potatoes on top. Pour in beef broth & sprinkle with thyme. Cover with foil & bake for about 2 hours.
Remove from oven, top with grated cheese, return to oven & bake uncovered for 15 – 20 minutes or until pie is golden. Remove from oven & serve with a vegetable of choice.