1: Preheat the oven to 210°C or 410°F. Pour 1 tablespoon olive oil into a tart mould or tin, spread it all over the bottom with a brush. Line this with 1 puff or flaky pastry (pâte feuilletée). If you have a protection paper with the puff pastry, leave it, and grease between paper and pastry. If needed cut around the top of the tin to remove excess pastry.
2: Prick the bottom of pastry with a fork all over to prevent it rising too much during cooking. Spread out 3 tablespoons mustard all over the puff pastry, with the back of a tablespoon or a brush. Leave to wait in the refrigerator.
3: Peel 6 tomatoes, and cut them in medium slices. Note: if you have the time (1 hour), salt them on both sides, and spread them out on a grid or in a strainer for aboout an hour, this draw out some of the juice could make the pastry soggy during cooking. See below on this subject.
4: Lay the best tomato slices around the bottom of the pastry case, as regularly as possible. Use a metallic spatula or a fork to place the slices, it's easier than with fingers.
5: Finish by filling the centre of the tart with the tomato offcuts.
6: Add a dash of olive oil (with herbs if possible).
7: If you have them, scatter some chopped herbs on the top, then put on a low shelf in the oven in the oven for approximately 30/40 minutes.
8: The tart is cooked when the bottom of the pastry is cooked, i.e golden brown. Best eaten warm.
9: Possible alternative: For a stronger tomato flavour, you can, after adding the mustard and before the tomatoes, add a layer of pizza sauce.
Remarks
The tomatoes depending on of their origin and ripeness could give off a lot of juice, which can be a bit annoying as it makes the pastry soggy. To try to reduce this there are several methods:
Do not salt before cooking, because it's the salt which brings out the juice. Instead salt salt just after bringing out of the oven.
Drain off as most of the juice partway through cooking, but it's a slightly delicate operation. For this Francoise uses a large plastic ex-medical syringe.
Salt the the tomatoes and leave the juice to drain off before using (see above).