Method

• 1.
  Preheat the oven to 200°C.

• 2.
  To prepare the pastry, place 1 sheet on a clean work surface lightly dusted with flour. Brush with beaten egg, then place another sheet of pastry directly on top. Smooth with a rolling pin, then roll out to a 35cm square. Cut a 28cm-diameter circle from the square. Transfer to a baking tray lined with baking paper and chill until ready to use. Repeat with remaining pastry sheets to make 2 tart bases.
• 3.
  Heat 2 x 25cm non-stick ovenproof frypans over medium heat. Divide the butter between pans and swirl to melt. Divide onion and sprouts between pans and arrange in a single layer. Cook, without stirring, for 5 minutes or until beginning to caramelise. Sprinkle with thyme leaves.
• 4.
  Combine sugar and vinegar in a jug, then divide evenly between pans. Cook for 5 minutes or until reduced and glossy.
• 5.
  Remove pans from heat and top each with a prepared pastry round. Tuck in edges to seal and brush with remaining beaten egg. Transfer to oven and bake, swapping shelves halfway, for 20 minutes or until the pastry is golden and crisp.
• 6.
  Carefully turn out tarts onto serving boards or plates, scatter with goat’s cheese and sprinkle with extra thyme sprigs. Serve tarts immediately with a lovely crisp green salad on the side.