Gorgonzola, Lardo, Basil, and Wild Rocket Tarts

Ingredients

• 1 tbsp extra-virgin olive oil, plus extra to serve
• 1 Spanish onion, thinly sliced
• 1 garlic clove, thinly sliced
• 100 gm Gorgonzola dolcelatte, crumbled
• 1 tbsp thyme
• 375 gm butter puff pastry sheet (see note)
• For brushing: eggwash
• 12 thin lardo slices (see note)
• 1 cup wild rocket (loosely packed)
• ¼ cup basil, coarsely torn (loosely packed)
• To serve: aged balsamic vinegar