Melt the butter in a frying pan and add the onion. Cover with the butter wrapper and cook over low heat for 5 minutes until soft but not colored.
Add the flour and cook until browned. Add the stock, bring to a boil and skim. Add the tomato puree, chopped parsley, thyme leaves, salt and pepper and simmer for 5 minutes.
Add the meat and peas/corn to the sauce and bring to a boil. Put in a pie dish, cover with the mashed potatoes and score the top with a fork. Reheat in a moderate oven (350 degrees Fahrenheit) for about 30 minutes. Garnish with parsley and serve with Irish Bread.