Preheat oven to 200°C.
Heat the oil and butter in a pan and fry the onions over a low heat for 12 - 15 minutes until they soften and turn a caramel colour.
Add the sugar, vinegar, salt and pepper and continue cooking for another 5 minutes.
Remove from the heat and allow to cool.
Roll out the puff pastry to a rough 20 cm x 30 cm rectangle, about 5 mm in thickness and place on a baking sheet.
Use a knife to score a 3 cm border around the rim of the pastry.
Scatter the Tussers Cheese in the central area, don't overlap the border.
Top with the onions, feta cheese and olives.
Bake for 25 - 30 minutes or until the pastry is crisp and puffed.
Sprinkle with thyme before serving.