Caramelised onion, courgette and Wensleydale quiche recipe

Ingredients

• 1 tbsp olive oil
• 15g butter
• 2 red onions, sliced
• 2 eggs
• 2 egg yolks
• 300ml double cream
• 100ml full-fat milk
• 2 small courgettes, around 225g, thinly sliced, lengthways
• 3 courgette flowers, sliced lengthways
• 175g crumbled Wensleydale cheese
• 300g plain flour, plus a little extra for dusting
• 150g butter, chilled and diced
• Pinch of sea salt
• Few thyme sprigs, leaves picked (optional)
• 1 egg, beaten