By William Lander, Shaun Searley and Daniel Morgenthau
This is almost effortless to prepare and makes for great summer lunch. Buy perfectly ripe tomatoes for their natural sweetness and flavour. We particularly like colourful, flavoursome Isle of Wight tomatoes. Good-quality puff pastry is easy to come by in shops; look for ‘all butter’ pastry.
Put the pastry discs on the tray, brush with egg yolk and score a circle 2cm in from the edge with the back of a knife – don’t cut all the way through the pastry. Spread a thin layer of Lyonnaise onions ins