See Notes for making ahead. Firstly, start with making the cheesy mashed potato topping - put the potatoes in a large saucepan of cold water, bring to the boil and add some cooking salt. Cook on a continuous simmer for 15 to 18 minutes until the potatoes are tender.
Meanwhile, brown the mince with 1 tbsp of olive oil over a high heat in a large saucepan or casserole. Once browned (this will take around 5 minutes), remove from the pan into a bowl and set aside.
Add the other tbsp of olive oil to the pan along with the onion, carrots and celery. Cook gently for about 20 minutes until the vegetables are soft, stirring occasionally.
When the potatoes are cooked, drain well in a colander and let them sit for a minute or 2 to steam dry. Meanwhile, add the milk and butter to the saucepan and put on a low heat to warm the milk and melt the butter. Turn off the heat and add the cooked potatoes. Mash well until the potatoes are smooth and the milk and butter combined. Season with salt, if needed, and black pepper, to taste and stir in the 65g of grated cheese. Set aside until needed at step 2 below.
Once the vegetables are soft, add the garlic, flour and tomoto puree, increase the heat and cook for 2 minutes, stirring constantly. Now add the browned mince to the pan and pour in the wine and reduce slightly (about 2 to 3 minutes).
Stir in the stock, Worcestershire sauce, thyme and bay leaf. Bring to a simmer and cook for 45 minutes, uncovered. Heat the oven to 180C/160C fan/gas 4.
Remove the thyme sprigs and bay leaf, stir in the peas and season with salt and freshly ground black pepper, to taste.