Artichoke Tarte Tatin with Red Onion and Hazelnut Dressing

Ingredients

• 3 small red onions, peeled and quartered
• 2 tablespoons olive oil
• 1 teaspoon flaky salt
• freshly ground black pepper
• 300 grams jerusalem artichokes
• 4 tablespoons caster sugar
• 1 sheet savoury short pastry
• handful torn radicchio leaves, to serve
• Hazelnut dressing
• 10 centimetre sprig rosemary, leaves only
• pinch flaky sea salt
• 3 tablespoons roasted hazelnuts, whole
• 2 tablespoons balsamic vinegar
• 1 tablespoon brown sugar
• 3 tablespoons olive oil