Ingredients:

FOR THE CARAMELISED ONIONS:

• 6 medium onions, finely sliced 
• 40g butter 
• 1 tbsp olive oil 
• 1 tbsp brown sugar 
• 1 tbsp balsamic vinegar 
• Salt & cracked black pepper 

FOR THE TARTLETS:

• 1 x 320g sheet of all-butter puff pastry 
• 100g Gruyère cheese, grated (or mature cheddar as an alternative) 
• 1 egg, beaten (for glazing – omit for vegetarian/vegan) 
• 1 tsp fresh thyme leaves (optional) 
• 1 tsp Dijon mustard 
• Mixed leaves, for garnish

Method:

1.  Heat butter and oil in a large pan over medium heat. Add the onions and a pinch of salt. Cook slowly for 25-30 minutes, stirring often, until soft, golden, and sweet. 

2. Stir in sugar and balsamic vinegar, cook for another 5 mins until sticky. Set aside to cool slightly.

3. Preheat oven to 200°C (fan 180°C). Cut the puff pastry into 6 10cm circles. Lightly score a 1cm border around each piece. Brush edges with beaten egg if using. 

4. Spread a little Dijon mustard inside each border. Spoon on the caramelised onions, then top with grated Gruyère and a few thyme leaves. 

5. Place on a lined baking tray and bake for 18-20 minutes, until puffed and golden. 

6. Serve warm with dressed winter leaves or a small spoon of tomato chutney on the side. 

* If you like a strong onion flavour, caramelise the onions for a further 15 minutes, until very dark brown.