1) Preheat the oven to 180 C.

2) In a large frying pan, heat a little olive oil and fry the chopped onion and garlic.

3) Add the mince, stirring, until browned all over.

4) While the meat is frying, break up any lumps with the back of the spoon.

5) Add the flour (this helps to thicken the juices) and stir.

6) Mix well and add the thyme and the rosemary and stir.

7) Add the chopped tomatoes and pour the stock mixture.

8) Add a pinch of salt and freshly ground black pepper and let it simmer for about 5 minutes.

9) For the mash, boil the potatoes, then drain them in a sieve and place into a clean bowl.

10) Add the milk, butter and egg yolk, and mash together.

11) Season with salt and freshly ground black pepper.

12) Pour the meat into an ovenproof dish and spread the mash on top, smooth over and mark with a spatula.

13) Put the dish into the oven and cook until the surface is bubbling and golden-brown.