Ingredients

• 1.15kg/2½lb red onions
• 25g/1oz butter
• 50ml water
• 1 tsp honey
• 1 tbsp thyme, chopped
• 1 tbsp balsamic vinegar
• salt and freshly ground black pepper

Pastry

• 140g plain flour, plus extra for dusting
• 70g butter, (cold)
• 50 ml water

Method

1. Cut in half lengthways from stem to root. After that, place the pan over a medium heat and, as soon as it’s hot, add the butter, vinegar, water and the honey, then as soon as the butter begins to sizzle, quickly scatter half the thyme in, then arrange the onions on the base of the pan, cut side down. As you do this you need to think ‘jigsaw puzzle’, so that after the onion halves have been placed in the pan to cover the surface, all of those left over need to be cut into wedges and fitted in between to fit all of the gaps. Bear in mind that what you see when you turn the tart out, is the cut side of the onions.
2. When the onions have all been fitted in, give them a good seasoning of salt and freshly milled black pepper, then scatter over a little more chopped thyme. Now turn the heat down under the pan and let the onions cook very gently for about 15-20 minutes until caramelising and starting to soften.
3. Place the pastry over the top, baste with milk and cook in the Oven/Remoska for 30 minutes. 
4. Leave for 10 minutes before turning out onto a plate and serving