Heat oil in a pan over medium heat, add onion, sugar and half the thyme, season and cook slowly for 15-20 minutes, stirring, until softened and coloured.
Remove from heat and allow to cool.
Preheat oven to 180°C.
Roll out pastry directly onto baking parchment on an oven tray.
Prick pastry with a fork, leaving a 3cm border.
Spread onion over the base, then top with the cheese and tomatoes.
Brush border with beaten egg.
Bake for 30 minutes or until pastry is golden and puffed.
Quarter the additional tomatoes and dress with the remainder of the thyme, salt and garlic oil, allow to macerate while the tart is cooking.
When the tart come out of the oven allow to cool slightly before dressing with additional tomatoes.
