For the peppers
In a bowl mix the peppers with the balsamic syrup and the olive oil and season with salt. Place the tart in the centre of a plate and serve with the roast peppers and a little more balsamic syrup.
For the tart dough
In the food processor’s mixing bowl, mix together the flour, butter, salt and sugar. Add the egg and water and mix until it forms a homogenous dough. Cover the dough with cling film and allow to rest in the fridge for 1 hour. Then, place dough in the centre of the tart shell and open with your hands beginning in the centre and pressing consecutively in all directions (up, down, right and left), until it forms an even dough approx. ½ cm. thick. Cover the dough with baking paper and some beans (to avoid the dough rising during cooking). Bake at 170°C for approx. 8 minutes, take out of the oven, remove beans and paper and cook for a further 4 minutes. Take out of the oven, allow to cool and then remove from tart shell.
For the filling
In the food processor’s mixing bowl, fold the chesses together until they are blended and slightly fluffy. Add the eggs and mix to create a light cream. Spread the caramelized onion on the bottom of each tart and pour over the cheese cream. Bake the tarts in a preheated oven at 150°C until the cream sets, approx. 10 minutes.