Heat a heavy-based pan or a dutch oven on medium heat and brown the mince until it releases its fat.
Add the olive oil and sauté the onions until lightly brown then add the garlic, and sauté for another minute.
Add the celery and carrots and cook for 5 minutes or until slightly softened.
Stir in the tomato paste and sprinkle on the flour. Give it a quick stir.
Deglaze the pan with port or red wine and let it evaporate.
Add the stock, Worcestershire sauce, bay leaves, thyme, salt, and freshly ground black pepper.
Give it a good stir and bring it to a boil.
Lower the heat and put the lid on. Let it gently simmer for 1 to 1 ¼ hours, until the meat is soft and the gravy has thickened. Stir every half an hour or so to avoid the sauce sticking to the bottom of the pan.
When the meat sauce is cooked, add the frozen peas and transfer them into an oven dish (approximately 25 mm diameter), and let it cool down for 30 minutes to avoid the mashed potatoes sinking in the meat sauce.