Line a 9-10” flan tin or rectangular baking tray with the pastry, and blind bake for 10 mins at 220 (200 fan).
Heat oil in a pan and fry onions and garlic gently for 5 minutes. Add mushrooms and fry for 2 more minutes. Mix in the tomatoes and herbs, and cook on a low heat for 30 minutes. If too liquid after this time, boil rapidly to reduce until fairly thick. Beat eggs with most of the cheese, reserving some to sprinkle on the top. Mix tomato mixture with egg and cheese, and add anchovy essence if using. Eason to taste.
Pour mixture into the prepared pastry case and sprinkle with the remainder of the cheese. Arrange anchovies on top, if paste has not been used. Lastly, add olives to decorate.
Bake at 220 (200 fan) for 15 minutes, then at 180 (160 fan) for a further 15 minutes. Eat cold.