The recipe for a great red onion, thyme and Parmigiano Reggiano tart

  1. A recipe of few ingredients but where technique is very important. Although not commonly instructed, it’s best to pre-cook the puff pastry to ensure it’s fully cooked and you’re not left with a layer of uncooked pastry, especially away from the edges. The combination of red onions and Parmigiano Reggiano gives an intense sweet-salty balance, with the flaky pastry giving necessary texture.
  2. Pre-heat the oven to 180°C (fan).
  3. Melt the butter in a heavy pan and sauté the onions over a low to medium heat, stirring frequently, until completely softened. This will take anywhere between 30 and 40 minutes. Season during and then check the seasoning at the end, as the eventual sweetness of the onions needs enough salt to balance the taste.
  4. Whilst the onions are cooking, prepare the pastry base. Oil an approx. 35cm x 25cm baking dish and dust with flour. Unroll the pastry and place on the baking sheet. With a sharp knife, score a 1-2 cm border around the edge of the pastry and prick within the border with a fork. Brush the border with egg. Bake at 180°C (fan) for 20 minutes. When removed it should be golden and puffed up.
  5. Increase the oven to 200°C (fan).
  6. Spoon the cooked red onions onto the pastry, within the border. The weight of the onions will collapse the pastry but it will be cooked properly. Cover the onions with the Parmigiano Reggiano then sprinkle the thyme leaves on top. Give the border another egg wash then return to the oven for 10 minutes. Remove when lightly browned on top.
  7. Best served after it’s been out of the oven for 15-30 minutes to allow to cool a little. Cut into four or six pieces and serve with a simple dressed green salad.