To begin making French Onion Tart Recipe, make pastry dough first. Add flour, salt, sugar  and butter cubes into a wide bowl. Using your fingertips break all the butter cubes and rub it with flour. Add chilled water little at a time and knead to make a smooth dough.

Roll the dough and cover it with cling wrap and place it in fridge for about 1 hour.

To make caramelized onions, heat butter in a wide pan. Add thin sliced onions into the pan and sweat the onions. Add salt and sugar, cook until onions are nice softened and browned evenly.

Add balsamic vinegar, lime juice and thyme; increase heat to high; boil for 2--3 minutes to reduce, stirring occasionally.

Take off the heat and set aside to cool.

To prepare the tart preheat the oven to 200 degrees centigrade and line a tart sheet pan with parchment paper.

Remove pastry from refrigerator and allow it to come to room temperature for 10 minutes. Divide the dough into equal portions and roll the dough to about 2-3 mm thick.

Place the dough on the prepared sheet pan and trim the edges. Refrigerate again for 10 minutes.

Fill a parchment sheet with uncooked beans (This is only to avoid the tart to puff up and later the uncooked beans are removed and are not the part of the recipe). Place it over the tart dough that will be baked.

Pop this into an own and bake for about 10 minutes or until you see brown spots on the tart.

Remove the uncooked beans parchment filling, and fill it with caramelized onions, sprinkle some more salt and pepper powder over the top and sprinkle some thyme leaves.

Bake in oven for about 15 minutes.

Serve French Onion Tart Recipe along with tomato ketchup.