Heat large saute pan over medium high heat. Spray pan liberally with cooking spray, then add 3/4 of the chopped onion, mixed vegetables and mushrooms. Cook, stirring constantly, for 2-3 minutes.

Add beef to pan and cook until browned. Add stock, bay leaves, tomato paste, Worcestershire sauce and season with salt and pepper.

Simmer gently for about an hour, until liquid is absorbed and thickened. Remove bay leaves, add fresh rosemary and stir to distribute. Remove from heat and allow to cool.

Preheat oven to 375 degrees. If desired, spray a baking dish with non stick spray and transfer beef and veggies mixture. You may skip this step if using an oven safe pan.

Cook potato with remaining onion in boiling salted water until fork tender. Drain, then return pot to stove and stir, allowing any remaining moisture to evaporate. Mash potatoes, adding milk, parsley, salt and pepper to taste.

Spread potatoes over beef mixture. Use fork to create a pleasing pattern, then bake 25-30 minutes or until potatoes are golden brown. If potatoes are reluctant to brown, broil briefly until browned. Watch carefully to prevent burning.