Preparation:
Preheat the oven to 200°C (gas mark 6-7).
Roll out the shortcrust pastry in a pie pan and prick it with a fork.
Brush the pie crust with the mustard evenly.
Flake the tuna and spread it over the mustard.
Wash and cut the tomatoes into thin slices, then arrange them on top of the tuna.
In a bowl, beat the eggs with the crème fraîche. Season with salt, pepper and herbes de Provence if desired.
Pour the mixture over the tart, then sprinkle with grated Gruyère cheese.
Bake for about 30 minutes, until the pie is golden brown.
Let cool for a few minutes before eating.
Tasting: Serve hot or warm with a green salad for a light and balanced meal! 
Enjoy your meal! 
