Prepare the shortcrust pastry. Mix the flour with turmeric, salt, sesame seeds, and butter cut into small pieces. Gradually add the water, mixing until a smooth dough forms. Shape the dough into a ball, wrap it in cling film, and refrigerate for at least 2 hours.
- Peel and slice the onions. In a large skillet, melt the butter with the olive oil, then add the onions. Season with salt and pepper. Cook over medium heat for 15 minutes. Sprinkle with sugar, stir, and cook for another 10-15 minutes over medium heat, until the onions are lightly caramelized. Let cool.
Take the dough out of the refrigerator 15 minutes before rolling it out. Preheat the oven to 180°C, gas mark 6.
Butter a 22/25 cm diameter tart tin. Roll out 2/3 of the dough to a thickness of 2 to 3 mm, line the tin with the dough, pressing it firmly against the sides.
Roll out the remaining dough to a thickness of 3 mm, and cut into strips approximately 1 cm wide.
Line the bottom of the tart with the caramelized onions. Distribute the Saint Agur Blue Cheese in small pieces over the onions, then arrange the strips of pastry in a crisscross pattern to form a grid.
Bake the onion tart for 30 to 35 minutes. Let the onion tart cool for 15 minutes outside the oven before slicing and serving. Enjoy warm!
