In an ovenproof casserole dish on the hob, heat the oil and add the finely diced onion, carrots and celery. Cook over a low heat for ten minutes, until softened and lightly brown.
Add the crushed garlic and thyme, cooking until fragrant (about 1-2 minutes) before adding the mince. Turn up the heat to medium and cook, stirring periodically until the mince is browned all over and juices caramelise on the bottom of the casserole dish.
Stir in the flour, tomato puree and Worcestershire sauce to the mince for a minute or so to combine. Immediately add the chicken stock, bringing to a simmer and cook for 10 minutes until the sauce is reduced and thickened.
Leave the mixture to cool for a few minutes and prepare the Mash Direct Cheesy Mash as directed. Top the mince mixture with the mash and smooth to create an even layer using the back of a large metal spoon.
Transfer the dish to the preheated oven and cook for 30 minutes, until the mash is a bubbling golden brown.