Method

• 1.
  Heat a large saucepan or deep frying pan over high heat. Add the onion, followed by the olive oil and thyme and cook, stirring, for about 4 minutes or until the onion is golden brown. Reduce the heat to low and add the butter. Continue to cook, stirring frequently, for 30 minutes or until the onion is dark brown and caramelised. If the mixture is oily, drain off excess oil. Then stir the port and bring to the boil. Stir through the vinegar and cook, stirring frequently, for 2-3 minutes until the liquid has thickened. Season to taste with and remove from the heat.
• 2.
  Preheat the oven to 200°C (fan-forced). Place the puff pastry on a baking tray and lightly score the edges of the pastry to create a 1.5 cm border – this allows the edges to rise during cooking. Spread the jammy onion over the pastry within the border, then lay the tomato slices over the top so they overlap each other. Season with salt and pepper, then brush the egg wash over the exposed pastry border.
• 3.
  Transfer to the oven and cook for 35 minutes or until the pastry edges are risen and golden brown, and the tomatoes are caramelised.
• 4.
  Drizzle a little olive oil over the tart and scatter with the basil and tarragon leaves. Divide the tart into quarters and serve with your favourite salad.