delicious hot or cold, and ideal for a picnic.
1 packet ready rolled puff pastry
750g red onions, peeled and thinly sliced
2 tbsp olive or rapeseed oil
3 sprigs fresh thyme
1 sprig rosemary
1 bay leaf 2 tsp soft light brown sugar
2 bundles British asparagus
1 egg, beaten
preheat the oven to 200°C/400°F/Gas Mark 6.
melt the butter with the oil in a saucepan. Add the onions, stir well to coat with the butter, cover and cook on a gentle heat, stirring from time to time, for 30 minutes, until the onions are completely soft. Add the herbs and sugar, increase the heat and cook until the onions are caramelised. Leave to cool, discarding the herb sprigs and bay leaf.
place the ready rolled puff pastry sheet on a lightly greased baking sheet. Using a sharp knife, score a 2cm deep border around the outside of the pastry, making sure you don’t cut all the way through.
trim the asparagus as necessary, and cut in half. Pile the caramelised onions into the centre of the tart and spread out to the inner edge of the border. Place the asparagus on top, season and drizzle with olive oil. Brush the border with the beaten egg to glaze and bake in the preheated oven for 20 minutes until the pastry is risen and golden brown. Turn the oven down to 180°C/350°F/Gas Mark 4 and bake for a further 20 minutes or until the pastry is cooked through.