|Frozen puff pastry||14 Ounce (400 Gram)|
|Gruyere cheese||5 Ounce (150 Gram)|
|Dijon mustard||4 Fluid Ounce (120 Milliliter)|
|Butter||1⁄2 Ounce (10 Gram)|
|Flour||1⁄4 Ounce (5 Gram)|
1. Thaw the pastry.
2. Bring some water to the boil and immerse the tomatoes for 10 seconds. Peel, cut them into quarters and remove the seeds. Remove the crust of the cheese and cut it into strips.
3. Preheat the oven to 250°C (475°F; gas mark 9).
4. Roll out the pastry to a thickness of 5 mm (1/4 inch). Butter a pie dish and sprinkle it with flour, then line it with the pastry. Spread a layer of mustard (1 cm/1/2 inch thick) on the bottom and cover with strips of Gruyere, then with tomato quarters. Sprinkle with oregano.
5. Bake for 30 minutes, checking from time to time to make sure it does not get too brown. Serve at once.