Add tomatoes, garlic, salt, and thyme to a heat-proof dish.
Pour the olive oil to cover the surface of the tomatoes.
Cook in the oven for 90 minutes to begin with; at this point, if the tomatoes have begun to burst and blister while still holding their shape, they are ready. If not, give them another 20 minutes, approximately.
Wash the jam jar in hot soapy water and put it in the oven to sterilise for 30 minutes.
Remove the sterilised jar and set it aside.
Once the tomatoes are soft and cooked, remove them from the oven and set them aside to cool for 10 minutes.
Transfer the cooked tomatoes into the sterilised jar and seal shut.
Let it sit on the kitchen counter to cool, then transfer to the refrigerator.
The nutritional information is for one complete 300ml jar of confit tomatoes. The number of servings per jar has not been given, as this will depend on how the confit tomatoes are used.